"New" Insight Into Behavior of Some Cuckoo Wasps (Chrysididae)

There is always something new to learn. That is the promise of entomology, and it is validated almost daily. Just last week (January 11) I came across this amazing image of Omalus puncticollis by Emily Hobson on my Facebook newsfeed. Since I know that many species of cuckoo wasps feed on the "honeydew" secreted as a sugary, liquid waste product by aphids and related true bugs, I suspected that the wasp in this photo was stimulating the little bug into producing some honeydew.

Female cuckoo wasps do not have stingers, so I knew that this was not a case of the wasp stinging a victim to then either consume herself or take back to a nest.....or so I thought. Cuckoo wasps are parasites of other kinds of wasps, and it turns out that this is what the wasp was up to, but indirectly.

One of the comments on the image revealed the extraordinary truth:

"This is really interesting. The species is probably Omalus violaceus, and the pic shows a behaviour, what is not formally described until now. The female Chrysididae wasp lays its egg into the Aphid. When a Crabonidae wasp (e.g. Pemphredon) takes the aphid as prey and carries it into its nest, then the chrysidid larva will appear earlier and develop in the nest instead of the larva of the crabronid wasp. Until now, many wasp researchers still think that the Chrysididae infect the host nest directly, which is not true. This behaviour is observed or suspected for Omalus and related genera, and for Holopyga." - Christian Schmid-Egger

So, the chrysidid wasp larva is a "cleptoparasite" that eats the food provided by the host wasp for its offspring. It literally steals from the mouths of the host larva, starving it to death.

These images were taken in Europe, but we have related species in North America, including a few that have immigrated from overseas as a result of accidental introductions on global commerce. I wrote about one such species, Pseudomalus auratus, in a previous blog post.

The comment thread from the Facebook "Entomology" group post reveals this might be the first photographic documentation of this behavior in this particular species, as noted by Alexander Berg, who also gives references:

"Actually it is described, for Omalus by Winterhagen P (2015), Holopyga by Veenendaal R (2012), and we also discuss it in Paukkunen et al 2015 (doi: zookeys.548.6164) for Pseudomalus (something Veenendaal has also postulated)....I don't think anyone doubts it occurs in all Pseudomalus, Omalus and Holopyga...."

Science and social media is becoming a marriage made in heaven, not only for informing the general public, but for communication between scientists, too. I am left now to wonder how much else I think I know, that I really don't know. In any event, you'll know when I know.

Special thanks to Emily Hobson for sharing her images, and for Christian Schmid-Egger for permission to use his quote here.

Wasp vs. Wasp

My wife and I went down to Fountain Creek Regional Park in Fountain, Colorado recently (the evening of June 2, 2013), and I happened upon an interesting scene. About five or six female mason wasps, Symmorphus sp., were nesting in beetle borings in a cottonwood log by the side of the trail. About four cuckoo wasps, Chrysis sp., were hanging out around the holes the wasps were using as nests. Heidi said I must have spent 45 minutes taking pictures of them all, but it was worth it because I got to observe what was happening.

The above image is one of only two really nice shots I got of the female Symmorphus mason wasps. They would alight near their nest hole, and dive in very quickly. If I approached too quickly with the camera, the wasp would fly off before entering. If I waited too long, I would get a shot of the wasp’s abdomen disappearing, or a seemingly empty hole. Waiting for the wasp to emerge was basically futile, as she would exit much more quickly than was possible to focus.

You have to have an appreciation of the size of the players and the beetle borings to know what I was up against. The borings are probably the exit holes of deathwatch beetles, family Anobiidae, which bore in dead, solid wood as larvae. The diameter of each hole is about the same as the end of a retracted ballpoint pen (about 3 millimeters). Yes, both the mason wasps and cuckoo wasps could fit through those holes.

”Science has strict rules against anthropomorphism, but if you ask me, those chrysidids were cunning and calculating.”

Meanwhile, the bright metallic green cuckoo wasps were not as easily disturbed as the mason wasps. They might run randomly around between holes, but most of the time they sat quietly in the vicinity of a group of holes. Science has strict rules against anthropomorphism, but if you ask me, those chrysidids were cunning and calculating. They were waiting for the wasps to show them which holes were active nests worthy of their attention.

Cuckoo wasps are parasitic in the nests of other solitary wasps. They can’t sting, but the last few segments of the abdomen of the female telescopes into an egg-laying organ that can reach into the bottom of one of those nest tunnels. The cuckoo wasp lays an egg in the nest of its host, and the larva that hatches generally consumes the meal intended for the host offspring.

In the case of Symmorphus, females catch and paralyze leaf beetle larvae that are free-living, or are leaf-miners (living between the layers of a leaf). At least one species of Symmorphus attacks leaf-mining moth caterpillars on occasion. The larval victims are packed into a cell along the length of the beetle boring, and the mother wasp lays her own egg on the last victim. She then creates a partition of mud or chewed wood fibers, and begins a new cell. The process is repeated such that several cells usually occupy one tunnel.

The mason wasps, for their part, were also quite cognizant of the cuckoo wasps. I witnessed at least one altercation whereby a female mason wasp fended off a too-eager chrysidid at the entrance to her nest. Cuckoo wasps, while they can’t sting, have a dense, pitted exoskeleton that effectively repels the bites and stings of their hosts. They can even roll into a ball as a last resort, becoming virtually impregnable.

Without collecting specimens of the wasps, which I did not do, I cannot conclude the species I was observing. Process of elimination narrows the possibilities to Symmorphus cristatus or S. canadensis for the mason wasps. The cuckoo wasps could represent one or more species in the Chrysis coerulans species group. Scientists are still trying to sort out how many species there actually are in that complex.

After getting up from my baseball catcher’s stance, I could feel how my legs had stiffened. The pain was worth the gain, though, and I encourage my readers to endure for the sake of personal and collective knowledge. Field observations are not the scientific priority they once were in the fledgling years of ethology (study of animal behavior). It could easily be you who makes history with a new host record for a predator or parasite, or records some other hitherto unknown association between species.

Sources: Bohart, R.M. and Lynn S. Kimsey. 1982. “A Synopsis of the Chrysididae in America North of Mexico,” Mem. Am. Entomol. Inst. 33: 1-266
Buck, M. Marshall, S.A., and Cheung, D.K.B. 2008. “Identification Atlas of the Vespidae (Hymenoptera: Aculeata) of the Northeastern Nearctic Region,” Canadian Journal of Arthropod Identification No. 5: 492 pp.
Krombein, Karl V. 1967. Trap-nesting Wasps and Bees: Life Histories, Nests, and Associates. Washington, DC: Smithsonian Press. 570 pp.

Wasp Wednesday: Pseudomalus auratus

At this time of year, we decorate the inside of our homes with festive ornaments, many of them green or gold or red. Nature offers her own ornamental organisms, but many are too small to grab our attention unless we look closely. Such is the case for the brilliant little cuckoo wasp, Pseudomalus auratus.

Cuckoo wasps in general are also known as “jewel wasps,” so colorful are they. This particular little gem averages only four millimeters in length, so despite its contrasting colors of emerald (head and thorax) and ruby red (abdomen), Pseudomalus auratus is easily overlooked. Rarely does this wasp visit flowers, either, so you have to seek it out elsewhere.

This species is not native to North America, but is common throughout Europe, Asia, and northern Africa. It was likely introduced here accidentally prior to 1828. Until fairly recently, records in the U.S. were limited to the Atlantic seaboard, but now it may turn up almost anywhere.

Larvae of this wasp are kleptoparasites in the nests of other solitary wasps, and solitary bees, that nest inside hollow twigs, pre-existing cavities in wood, and similar situations. Known hosts include the smaller wasps in the family Crabronidae, and bees in the genera Ceratina (small carpenter bees, family Apidae), Hylaeus (masked bees, family Colletidae), and Anthidium (wool-carder or cotton bees, family Megachilidae). The cuckoo wasp grub feeds on the provisions stored by the mother of the host larva. They literally steal the meal provided by the host for its offspring.

Pseudomalus auratus is not without its own enemies. Parasitic wasps in the families Ichneumonidae and Torymidae are known to kill the larvae, though those casualties might be the result of the parasites attacking the same host as the cuckoo wasp.

Look for adults of the cuckoo wasp around aphid colonies and extrafloral nectaries on various plants. I found specimens in Ohio at aphid colonies on Honeyvine Milkweed (Ampelamus albidus) and Northern Catalpa (Catalpa speciosa). The specimen shown here is from Colorado Springs, found sipping on the tacky exudates of Common Sunflower (Helianthus annuus).

Please share your own observations of this species with the scientific community. Our understanding of the distribution and hosts for Pseudomalus auratus in North America is in its infancy.

Sources: Agnoli G.L. & Rosa P., 2012 : Pseudomalus auratus (Linnaeus, 1758) . In: Chrysis.net Database of the Italian Chrysididae, interim version 12 December 2012.
Species page at Discoverlife.org.
Species page on Encyclopedia of Life.
Bohart, R.M. and Lynn S. Kimsey. 1982. “A Synopsis of the Chrysididae in America North of Mexico,” Mem. Am. Entomol. Inst. 33: 1-266 (Note: species is listed as Omalus auratus).

Cuckoo for Cuckoo Wasps

You would be hard-pressed to find lovelier insects than the cuckoo wasps of the family Chrysididae. They are clad in gem-like colors of emerald, ruby, jade, and even copper and gold. These wasps are small, and stingless, too, making them much less intimidating than other members of the order Hymenoptera.

The life histories of these unique insects remind one of a spy thriller or great crime caper. While a few obscure, tiny cuckoo wasps parasitize the eggs of walkingstick insects, most female cuckoo wasps lay their eggs in the nests of other kinds of solitary wasps, or solitary bees, exposing themselves to the jaws and stings of much larger, stronger species. The cuckoo wasps have what amounts to a “bulletproof vest” in their extra thick exoskeleton that acts like a suit of armor. The wasps can also roll themselves into a compact ball to protect their faces, legs, and other vulnerable body parts, much like a turtle or tortoise can retract into its shell, or an armadillo rolls up.

That durable cuticle is pitted, grooved, and otherwise sculptured, creating facets that reflect various wavelengths of light and give the insects their bright metallic colors. Pigments have nothing to do with their jewel-like quality.

Different species of cuckoo wasps have different “hosts” for their larval offspring. Some species specialize in breaking and entering the nests of mud daubers while others spy on wasps that dig nest burrows in the soil or sand. When the mother host species is away from the nest, the cuckoo sneaks in to lay her own egg. She has special, telescoping abdominal segments that complement an egg-laying organ called an ovipositor, helping her to hide her egg among the paralyzed insects or spiders harvested by the host wasp as food for its own larvae.

The egg of the cuckoo wasp hatches after the larva of the host species. The cuckoo larva then attaches itself to the host larva, and waits patiently as the host larva eats and grows, reaching the “pre-pupal” stage. At this point the cuckoo larva begins consuming the host larva, eventually killing it in the process. The mature cuckoo larva then pupates and emerges from the nest as an adult cuckoo wasp sometime later.

An alternative life history is found in some species where the cuckoo larva eats the host’s egg or young larva, then scarfs down the food stored for the host (paralyzed insects, spiders, or pollen and nectar).

Adult cuckoo wasps fuel themselves on carbohydrate-rich foods. Oddly, few species seem to visit flowers with any regularity. Instead, you are more likely to find them around aphid colonies, lapping up the “honeydew” excreted by the sap-sucking aphids as a sugary, liquid waste.

Cuckoo wasps can also be found on the exterior of old barns, on dead, standing trees, and similar situations where they hunt for the nests of their hosts.

Chrysidids are more diverse in western North America than they are in eastern North America, but are often harder to find in the west. Few resources exist to help you to identify them, either, though there is a wonderful new interactive key to Cuckoo
Wasps of Eastern North America at Discoverlife.org. The website BugGuide.net also has many images of cuckoo wasps sorted at least to the level of subfamily or tribe. The best internet resource is devoted to European cuckoo wasps and is dubbed ”Chrysis.net.

By all means, enjoy searching for cuckoo wasps in your own backyard, local parks, and elsewhere. There is still much to be learned about them and room for scientific contributions from everyone.