Ruby tailed or Jewel wasps the beautiful cuckoos

Chrysidids. Beautiful Ruby-Tailed or Jewel wasps

That flash of iridescent metallic blue-green you observed near your solitary bee nest box was probably a wasp. It is likely to be a Chrysidid cuckoo wasp, a family of parasitoid and cleptoparasitic wasps. Their beautiful colours mask the intentions of this assassin. Or in some cases, it could simply be a thief! Why the confusion?  Read on!

I generally see them on hot sunny and dry days in my garden, over the summer months, either walking on or flying along skirting brick walls, stopping to investigate small holes and cracks they find. They also loiter around my solitary bee nest boxes, entering or investigating nest cavities.

Cuckoo wasps. Cleptoparasite or parasitoid? 

Many people call these wasps parasitic wasps. This is not strictly true. Parasites will live at the expense of their hosts but do not kill it. Parasitoid wasps nearly always kill its host. The larvae can develop inside or outside of its host, either way, the host dies.

The Royal Entomological Society (RES) puts their larval biology nicely, “ The chrysidid larva may first destroy the host egg or young larva, and subsequently consume the cell’s food store, or it may consume only the mature host larva. Individuals with a mode of life intermediate between parasitism and predation are known as parasitoids and feed upon or within the living body of another organism, eventually causing its death. The term cleptoparasite is also used by some to describe those chrysidids which develop largely at the expense of the host food store. The chrysidid larva usually devours the host egg or young larva before consuming the host food store”. It continues,”The majority of chrysidids are parasitoids of wasps and bees which nest in the ground, cavities in wood or which build mud cells.” “The size of the adult is certainly influenced by the host size”, which makes sense.

Cuckoo 

Like cuckoo birds, most of these wasps waste no time on parental duties or even making nests, unlike their hard working dutiful hosts. Although to be fair these females have different needs to satisfy. Many parasitoid species use carbohydrates for body maintenance and can extend their life expectancy many times by regularly replenishing their sugar reserves. They need to allocate their time between host and sugar foraging based on the tradeoff between current and future reproduction. Then spend time finding a suitable host site, ensure it is appropriately provisioned, infiltrate the cell, oviposit, then escape unharmed! It’s no wonder that once they find a suitable host, they will return to it, even after being chased away by the host.

Fuel or host forage?

In other words whilst they are host-foraging which will increase the likelihood of finding a suitable host, it continuously decreases its energy reserves and consequently life expectancy. Whereas fuel foraging postpones ovipositing opportunities, whilst increasing the time available to find hosts in the future by replenishing its energy reserves. Besides her physical condition and age, even the weather such as wind would also expend more energy as she flew. I have seen such wasps feeding upon honeydew on flowers where aphids are present. It’s all a critical balancing act.

Honeydew

However, it turns out that honeydew has been found to be poorer in quality compared to floral nectar with regard to life-time extension. Nectar can vary in quantity, depends upon the time of the day, climate and competition from other nectar forages. Borage is worth taking note of here as a nectar food resource. Goulson states, “For example, borage produces nectar very fast, whereas comfrey is middling, and birds food trefoil is very slow. When feeding on borage, bees start revisiting a flower just two minutes after the previous visit, and again this roughly corresponds with the time it takes to refill. If parasitoid wasps could read this!

Closer examination

If you look at a specimen closely, you may also see metallic shades of red, purple or even gold depending upon the species, with what appears to be numerous tiny pits or tiny indents on their bodies.

Species and hosts

The RES states in Britain, the Channel Islands and Ireland they are 33 species. Enough said for me, I will leave that to the experts who study them to identify them! They also state that the larvae of British species, develop in the cells of solitary bees and wasps and in the cocoons of sawflies. Martynova states that Chrysidis wasps may be considered the most common enemies of Eumenine wasps  (Potter or mason wasps).

“The females of these cuckoo wasps (e.g. Ch. ignita) lay an egg in the host cell (e.g. potter wasps) at the last stages of provisioning. The few existing data points to the fact that the young inquiline larvae kill the egg or the young host larva and only after this set to feeding on the stored provisions.” This means that the wasp larva is a parasitoid when it kills or eats the host egg, larvae, prepupae or even pupae. It then becomes a cleptoparasite when it feeds on the host provisions, such as sawfly larvae, beetle larvae, or caterpillars.

Finding a host

As they fly along brick walls using their antennae (feelers) they vibrate repeatedly, (antennating) especially in or near the presence of a potential host nest site, or a stored food source in a solitary bee or solitary wasp nest cavity. Their antennae have sensitive receptors which pick up olfactory odours from their hosts. According to Wisniowski, even now in Europe, the biology of these wasps and their hosts there is little data. Martynova (2017) continues with this,” The biology of Chrysididae is poorly known in general. Usually, only the name of the host is reported. There are only a few species with fully described life cycles. Some of the data on host-parasitoid associations are doubtful since they were obtained during field observations (e.g., a female cuckoo wasp was seen entering into the burrow of a “host”). Only direct rearing from host cells, cocoons, and eggs gives reliable data on host-parasite relationships. Artificial trap-nests appear to be very useful while studying the biology of chrysidid wasps.”

Self-defence experts

Having a rather risky life cycle, O’Neill describes them as being exceptionally well armoured. They are capable of curling up into a tight ball when attacked, which comes in very handy if you are trapped inside a nest cavity and the female owner returns to find you! They have a thick, smooth and hard exoskeleton which makes it hard for attackers to grip tightly when defending their nest cavity. Although I note that their wings may well be exposed and may be damaged.

Do these wasps sting?

Although they have a sting, it is used as an ovipositor, and not used for defence or for stinging prey. I have never seen them chew a hole into the mud sealed cavity to gain access to lay an egg. Nor use their ovipositor to gain access to a sealed mud cell. Unlike Monodontomerus wasps which will use their flexible ovipositor to gain access through the mud to oviposit inside a cell. The RES states this about the sting of Chrysis ignita, ” Its effectiveness is certainly reduced as the telescopic tube bends in Chrysis ignita when the sting unsuccessfully tries to penetrate human skin (personal observation)”.

Persistent wasps

Any nest entrance left open and unsealed by the host is vulnerable when the host female is out. I have seen cuckoo wasps enter occupied nest cavities and watched the owner chase the wasp out or push the now balled wasp out of its cavity. Remember some nest cavities can be narrow so seizing it in its mandibles to eject from the nest could be difficult. In many cases, though the wasps simply move way a little distance and once the owner has left to forage, it will enter again. You can see in the video the cuckoo wasp watch its target host solitary wasp completely unhindered by the host.

Parasitic biology

According to BWARS, Chrysis viridula uses the solitary wasps Odynerus spinipes as a host for its larva. “Ch. viridula usually acts as a cleptoparasite, entering either the unsealed cell or removing the partition of a provisioned cell and laying its egg. The larva on hatching destroys the host’s egg before eating the prey. However, it may also act as a parasitoid feeding on the mature larva of its host”. O. spinipes, also known as the spiny mason wasp, takes weevil larvae for its larvae. When a Chrysis wasp larva hatches it feeds on the host egg or larva or on the closest prey stored in the host cell.

Martynova (2014) describes how Ch. viridula penetrates into the potter wasp nest as they cannot penetrate the cells when completed by the potter wasp. Thus they have to enter before the cells are completely sealed or lack the additional protective layers that cover the whole nest.

In the video, I believe the jewel wasp (possibly a Chrysis ignita?) is making a reconnaissance of the other solitary wasp’s Symmorphus-bifasciatus?  nest site and it often went inside the active cavity. As there is no pollen inside to steal for its own consumption, I can only assume the jewel wasp was checking out the cavity of a potential host in order to lay its own egg. Timing is critical as it has to be laid when the host is away leaving an empty cell, breach an unhardened mud cell, or before the cell is mud sealed and hardened.

Carnivorous larvae

According to O’Neill, unlike other carnivorous insects, which when they hatch, they are completely mobile, efficient at finding and subduing prey items, e.g. ladybirds, solitary wasp larvae are supplied with food by the female wasp. Most solitary wasps larvae are carnivores of insects.

Mandibles

Being carnivores, most wasp larvae hatch immediately after being deposited and commence feeding on the host or killing the egg. To do this they have to be equipped with suitable mandibles. I note that the Coelioxys cuckoo sharp-tailed bee larvae I filmed had sharp sickle-like mandibles, which the larvae will loose when it moults as it would be incapable of consuming the liquid/nectar mix inside the leaf cutter cell.

Red Mason bees as hosts

According to BWARS, Chrysura radians use Red Mason bees as a host.  On the Osmia bicornis page, it states, “Nests of this species are invaded by the following hymenopterous cleptoparasites and parasitoids: Chrysis ignita.” Similarly the same is stated by Wikipedia and Buglife. Interestingly Wisniowski states that Ch. ignita uses a large variety of solitary wasp species, which includes several Symmorphus species and makes no mention of O. bicornis being a host of Ch. ignita in Poland and states that O. bicolour is a doubtful host. I suspect the wasps I have observed on many occasions may be Ch.radians and Ch. ignita.

Pollen Robber!

Wisniowski, states, “There is also some erroneous information published about the biology of Chrysididae and the source of errors are misinterpreted observations by various authors. The presence of a cuckoo wasp around a bee or wasp nest does not automatically indicate the real relations between the two species. It is known that cuckoo wasps sometimes enter wasps of various solitary bee species to steal some pollen stored in the cells.” Similarly, Martynova states “Data or suggestions based on observations of cuckoo wasps which showed activity near the host nesting places or penetrated into the host nests deserve special consideration. Such data should be interpreted with great caution, all the more so that, as pointed out by Buysson (1891-1896)  adults of many cuckoo wasp species feed as ‘marauders’ on the mixture of pollen and nectar stored in provisioned cells of bees”.

Falsely accused and mistaken identity!

I am guilty of this absolutely! Their intention as stated above is to steal food for themselves, not to lay an egg for its larva to kill the bee larva! This is a revelation to me, I automatically thought these beautiful wasps were all out to parasitise my bees every time! They, as adults can be opportunistic cleptoparasites. Its likely that the species I have observed may well be a species that uses solitary wasps and their provisions as its host, but nips into solitary bee nests as a ‘marauder’ for a quick snack!

Chrysura species

Dr K Martynoa, a specialist in Chrysididae wasps, (pers.comm)

“Generally cuckoos of the genus Chrysura are the specialized parasites of bees in the genus Osmia and some other taxa. They have an unusual way of development, the “metaparasitism”.

“The specific trait of metaparasites is delayed development of the larvae, although these wasps lay an egg into the host cell already at the provisioning stage (almost simultaneously with the oviposition of the host), the larva of the metaparasite begins to eat the host larva only after it has consumed all the provender, reached its maximum size, and completed its cocoon, i.e., at the pre-pupal stage. This is characteristic of cuckoo wasps developing in bee nests. This behaviour of the cuckoo wasp larvae is adaptive because, being carnivorous, they cannot consume the provender of plant origin (pollen and nectar) themselves and have to wait until it has been eaten by the host. Since metaparasites eat the already cocooned host larva, their own cocoons occur inside those of their hosts”.

She continues,” All larvae of cuckoo wasps are carnivorous, they never consume ‘plant food” (pollen or nectar). If it is a bee nest a cuckoo wasp may feed only on the bee larva. If it is a wasp nest it can feed on the wasp larva or on its provisions, spiders, cockroaches, thrips, aphids etc.”

It’s probable that I have observed Chrysis wasps as they enter my Osmia bee species cells believing they are cuckoos when they are stealing pollen and when a Chrysura has entered it is either ovipositing or feeding on the pollen. They look identical and I would not be able to identify them. It appears now to me after my researching that Chrysis wasps may not use bees as hosts at all as they need the paralysed prey items, to feed upon and there is no pollen inside the cells. Chrysura certainly does use bees as hosts, where pollen and not prey items are stored. Initially, they do consume pollen. But they cannot develop on pollen or nectar. Instead, they wait for the bee larva to consume and process it into useable food ( i.e. convert it via its body fats and fluids!) then it itself is consumed.

Different strategies for larva emergence

When a cuckoo wasp lays an egg in another solitary wasp nest that has been provisioned by the host female, the cuckoo wasp larva usually emerges BEFORE the host wasp egg. The cuckoo after emergence seeks out the host egg/larva and kills it, continuing to consume the provisioned prey items. If a cuckoo wasp invades a Red Mason bee cell, it has a slightly delayed emergence. If the carnivorous larva immediately sought out, killed then consumed the bee larva/egg, being a carnivore it has no interest in the remaining pollen/nectar provisions. It will die due to a lack of food. The larva of Chrysura species has a different tactic.

Host prey item consumes pollen

The RES quotes “A study by Krombein (1967), which covered some of the North American species, found that the chrysidid larva usually hatched a day later than the host bee and sometimes consumed a small amount of ”nectar”. About 3-7 days after hatching, the Chrysura larva attached itself to the feeding bee larva and slowly began to consume it. The host bee larva began to spin its cocoon 17-31 days after hatching. As soon as the host cocoon was completed and the bee larva quiescent, the Chrysura larva moulted to the second instar and then completely devoured the host. The Chrysura larva then spins its cocoon inside that of the bee.”

Krombein (1967)

I wanted to delve a bit deeper into this subject. It was one of those “wow!” moments you occasionally get! A study by Krombein (1967), which covered some of the North American species, is well worth reading if this kind of topic interests you. Osmia bees are parasitised by Chrysura wasps who have synchronised their development perfectly with that of their bee hosts, transforming concurrently, overwinter in their cocoons and emerge concurrently with the bees the following spring.

How successful a cuckoo wasp was could depend upon how skilled it was in concealing its egg from the hosts. Presumably, then a cuckoo wasp egg hidden in a pollen-mass would be easier to conceal than an egg deposited upon a paralysed prey item?

The egg usually hatched a day later than the host bee, even though both eggs were presumably deposited on the same date. The newly hatched larva moved slowly over the pollen mass stored for the host bee; occasionally it appeared (my italics) to imbibe a small amount of nectar. About 3-7 days after hatching, the first instar Chrysura larva attached itself by its mandibles to the feeding bee larva and slowly began suck a small amount of blood, but does not increase greatly in size, nor does it moult to the second instar until the host has finished feeding.

So in effect, the cuckoo wasp larva in its first instar is literally acting as a parasite whilst attached to its host bee larva as it feeds on the pollen. Just taking a little blood for it to survive and keep it ticking over. Wherever the bee larva goes, it goes.

The host bee larva began to spin its cocoon 17-31 days after hatching, the Cuckoo wasp larva is still attached by its mandibles, it had now increased in size and was turgid, but it had not moulted. As soon as the host cocoon was completed and the bee larva became quiescent, the Chrysura larva moulted to the second instar and began to feed on the host larva which was usually devoured completely. Then the Chrysura larva spun its own cocoon inside that of the bee cocoon.

Ouayogode (1979) states some interesting tidbits from this large paper!

Hicks (1933) describes how the Chrysura larva held on to the bee cocoon through all the motions of cocoon spinning by means of its jaws, supplemented times by the contact of the posterior end of the body.

Ferton (1905) describes how two Chrysura larvae fight with one another, with one killing and sucking its the nutrients from its rival, to then suck three drops of the host fluid before resting.

Fernald (1920) reports that to control an Oriental moth infestation in Massachusetts, Chrysis shanghaiensis was introduced from China in 1921. (Nowadays a native N. American leafroller parasite has adapted to this moth)

When Chrysura larvae attached themselves to the bee larva, the bee larva continues actively feeding on pollen and defecating. They attached themselves to the back of the host at any point behind the head, using the sharp points of the sickle-shaped mandibles, without complete penetration, avoiding areas readily reached by the host’s mandibles. It ceases all movement unless disturbed. It is carried in a piggy-back fashion. A detailed description follows about the Chrysura larva feeding and moulting.

First instars Chrysura consumed small amounts of pollen and fed briefly on the host, without any apparent harm to the host.

The shape and function of the mandibles changed with each moult in all species. Initially, they were sharply pointed, sickle-shaped, and sclerotized. They projected from a prognathous head. Their shape appeared to aid in the hatching process and enabled parasites to puncture hosts, eggs, or prey. Their position helped in aggressive encounters with competing chrysidid larvae.

Exiting the Red Mason bee cells.

I would imagine that the adult Chrysura wasps inside Red Mason bee cells would either have to await the arrival of adult bees emerging behind them to chew through the mud capped walls or perhaps do this themselves?

Flowers visited by Chrysidids

They visit plants of many families with most records showing the carrot family *Apiaceae, spurge family Euphorbiaceae, and the aster family Asteraceae. Wild carrot, ground elder and yarrow prove popular for nectar. Aphid honeydew is also used as nourishment. So by planting

Angelica, wild carrot, hemp agrimony, asters, spurges, ground elder, ( which can be invasive) yarrow and a variety of open-structured flowers, you may see them foraging.

My conclusions!

I decided to spend some considerable time researching this topic to enable others to make more informed choices. I had no intentions to do this at initially, I wanted to link to my new product as set out below! Although I did find it fascinating and intellectually stimulating! I am now of the opinion that Chrysura wasps target solitary bees as hosts and Chrysis wasps target solitary wasps as hosts. They are not always out to kill my bees as this besides depending on the species, they may just be stealing some pollen/nectar mix.They are part of nature and fascinating to study.

Now available. Summer solitary bee and solitary wasp nesting unit

This new unit will allow you to watch for yourself, the comings and goings of such episodes as the ones described above. But you have to be fast to catch them laying their eggs!

Besides my own experiences, observations and various website links above, references, further reading and useful resources:

BWARS Chrysidid species gallery

Goulson, D, (2014) ” A Sting in the Tale”

Krombein, K.V. (1967) ” Trap-Nesting Wasps and Bees. Life Histories, Nests and Associates.”

Morgan, D.  (1984) “Handbook for the Identification of British Insects- Cuckoo-Wasps” Royal Entomological Society;

O’Neill, K. (2001) “Solitary Wasps. Behaviour and Natural History” Cornell University Press

Ouayogode, B.V. ( 1979) “Larval Biology of some Utah Chrysididae” Utah State University

Tenhumberg, B. et al (2006) “Optimal time allocation in parasitic wasps searching for hosts and food”.

Wisniowski, B. (2015) Cuckoo-wasps of Poland

Ruby-tailed wasp article by Buglife

Ruby-tailed wasps article here  RES

Interesting solitary wasp photographs by Steven Falk

With thanks to S. Falk, J Early and Dr K Martynova.

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