I was asked to talk about wasps over on tumblr, and I put so much effort into the resulting post that I figured I’d better cross-post it over here, too.
The fear of wasps and bees is an incredibly common phobia. For anyone who’s ever been stung by a yellow jacket or a hornet, this probably seems like a perfectly reasonable thing. Being stung hurts, and some people can have life-threatening allergic reactions to stings. And unlike bees, wasps don’t get a lot of positive press. They don’t make honey, after all, and they’re not the insects that we think of when we think of agricultural pollination.
But wasps are probably some of the most important insects in the world. If we somehow managed to remove all of the wasps from the world, it wouldn’t be inconvenient or a small ecological disaster, but the world would basically stop working.
This post is going to get long, but hopefully by the end of it, I can convince you that wasps are the best animals ever.
Vespula sp., Image by Matteo di Nicola
So, the first thing that you need to understand about wasps is that wasps are really diverse. The term ‘wasp’ is pretty broad, and is basically used to mean any insect in the order Hymenoptera that is not an ant or a bee. And by that definition, there are well over a hundred thousand species of wasp on the planet. In fact, the wasps, ants and bees are the fourth-most-diverse group of insects on the planet after beetles (~300,000 species), the butterflies and moths (~150,000 species) and flies (~150,000 species).
It’s also really important to note that wasps are the only hyper-diverse group of insects that’s predominantly carnivorous. While there are some carnivorous beetles, most of the beetle diversity occurs in herbivorous groups, like the weevils. Lots of these beetles are important agricultural pests. Butterflies and moths are also mostly herbivorous, and their caterpillars consume a truly shocking amount of vegetable matter. Flies are a little more diverse in their eating habits, and include scavengers, detritivores, predators, but also quite a few herbivorous groups. The fifth largest order of insects, the true bugs, is primarily represented by plant parasites like aphid and leaf hoppers.
And wasps are one of the primary population controls on these hundreds of thousands of species of herbivores. Other animals, like spiders, birds and frogs do their part in eating pest insects, but none are so incredibly specialized and effective as the wasps.
There are a lot of other good reasons to love wasps. For example, they are really good models for understanding the evolution of social behavior, and some species are important pollinators. Some species of wasps have evolved symbiotic relationships with viruses as part of their reproductive strategy, while other kinds of wasp have been used as part of famine-relief strategies.
So, here’s a little tour of some representative wasp diversity (with pictures!) in order to convince you that wasps are really awesome.
Sawflies and Horntails (Subfamily Symphtya)
Birch Sawfly, Image by Eric Begin
Okay, remember all that stuff that I just told you about wasps? Forget it, because this group of wasps breaks all of the wasp rules. In this group, the adults are incapable of stinging. Instead, their long ovipositors are adapted to saw into the stems of plants, where the females will lay their eggs. When the babies hatch out, they look almost like butterfly caterpillars, and they fill a very similar ecological niche, chowing down on leaves and other plant matter, before metamorphosing into adults. Many of those adults are nectar-feeders, which means that they play an important role in pollination, although some species are carnivores.
Parasitic Wood Wasps (Family Orussidae)
Chalinus braunsi, image from WaspWeb.org
A super, super interesting group, the parasitic wood-wasps share many features with both the sawflies (suborder Symphyta) and the narrow-waisted wasps (suborder Apocrita). Superficially, they resemble sawflies, but their larvae, like the larvae of many, many Apocritan species, are parasites on wood-boring beetles. Scientists think that these wasps might be a good example of an important transitional step in the evolution of wasps,
Sand Wasps (Family Crabronidae)
If you live in North America, you are probably familiar with the cicada killer wasps (Sphecius spp.). These are some of our largest wasps and can grow up to two inches in length (~5.0 cm). Every summer, when cicadas emerge, the females will hunt down the cicadas, paralyze their prey by stinging, then bring the cicada to a next they’ve dug in sandy soil. Even though these wasps appear frightening, they are not aggressive, and can even be gently handled.
Another, even potentially more awesome sand wasp is the Horse Guard Wasp (Stictia carolina). Their life cycle is very similar to the cicada killer’s, but instead of cicadas, they prey on biting horse flies. These wasps may kill up to fifty flies to provision a single nest … and if you’ve ever been bitten by a horse fly, you can probably appreciate just how wonderful these wasps are.
Thread-Waisted Wasps (family Sphecidae)
Sceliphron caementarium, Image by A. Jaszlics
Like the sand wasps, this really diverse family of wasps use stingers to paralyze prey to feed to their babies. Some of these wasps are pretty impressive architects — mud daubers like this one, for example, build mud borrows on the side of rocks, cliffs, buildings and bridges. While most of these wasps provision their burrows with enough prey for the developing larva, and then leave the grub to its fate, some species will actually continue to hunt for their developing young as they grow. The sphecids are also pretty cool, because they’re one of the first evolutionary lineages of wasps where we see social behavior starting to develop — for example several female Microstigmus wasps will come together to build a communal nest, instead of having each female construct an individual nest.
Cuckoo Wasps (Family Chrysididae)
Cuckoo Wasp, Image by Kevin Collins
Also known as jewel wasps, the cuckoo wasps are one of the most beautiful groups of wasps, with iridescent blue and purple bodies. They’re actually one of only a few groups of wasp that’s physically incapable of stinging — to defend themselves, they will roll up tightly into a ball instead. As the name suggests, though, these are wasps that like to leave the job of rearing their young to other insects. Mother wasps will sneak into the nests of other insects, where they lay their eggs on to of the developing larvae. When the baby cuckoo wasp hatches out, it will first eat the host larva, and then consume any provisions that might have been left in the nest. Pretty is not nice!
Velvet Ants (Family Mutillidae)
Array of Velvet Ants, Image by Robyn Waayers
Velvet ants are some of my absolute favorite wasps, because they’re just so weird! The females are wingless and look like very furry ants, while the males have wings. As adults, both sexes feed on nectar, and they may play an important role in the pollination of some desert plants. The females sting and paralyze the larvae of ground-dwelling insects (especially bees), then lay their eggs on the outside of the paralyzed grub — when the baby velvet ant hatches out, it consumes its still-living host before metamorphosing. Velvet ants have one of the most painful stings of any wasp (some species are called cow killers for this reason). Oh, and if you (very carefully) hold a velvet ant up to your ear, you may be able to hear it squeak, which is one of the awesomer entomology experiences in this world. (Yes, I have done this.)
Spider Wasps (Family Pompilidae)
Pepsis sp. with prey, Image by Robyn Waayers
How do you feel about very large, furry spiders? Okay, hold that thought.
How do you feel about the fact that there are wasps who kill tarantulas to feed their young? Tarantula hawks in the genus Pepsis develop as parasites on paralyzed tarantulas, which means that mother tarantula hawks must attack, sting and paralyze tarantulas before dragging them to their burrows, where they will lay a single, tiny egg on the enormous spider. The larva hatches out, and begins to devour the spider from the inside out … while avoiding the major organs to keep the spider alive and fresh. As adults, they are fairly innocuous, non-aggressive nectar feeders … but when provoked, they deliver one of the most excruciatingly painful stings in the animal kingdom, which one biologist compared to “a running hair drier […] dropped into your bubble bath.” Other spider wasps have a similar life cycle, and are parasitic on every kind of spider from tiny jumping spiders to large wolf spiders.
Fig Wasps (Family Agaonidae)
Fig Wasp, Image by Mike Gordon
Whenever I start talking about wasps, I feel like I spend a lot of time talking about the amazing diversity of horrible parasites, and while this is an important part of wasp diversity, I think that we should also take the time to appreciate the fact that there’s a lot of other, really, really weird diversity that goes on. A really great example of this are the fig wasps. The 800+ species of figs are a major component of tropical ecosystems, and are a keystone species, providing fruit and habitat for countless species. And almost every species of figs relies on a mutualistic relationship with the fig wasp in order to pollinate itself and bear fruit.
In these wasps, the males are flightless, doomed to live, mate and die inside the flower (technically an inflorescence, consisting of multiple flowers) where they were born. The females, by contrast, will mate inside of the fig flower, before leaving through an escape hole chewed by the male. They’ll then disperse to a new flower, which they pollinate by entering a small hole in the fig flower. Crawling into the flower is a traumatic process, and tears up the female’s wings, leaving her unable to escape the new host flower. Here, she lays her eggs, which will develop into a new generation of wasps. The fig itself ripens after the new generation of wasps has left, so that it can be eaten by frugivores, and have its seeds dispersed.
If you’re terribly worried about eating dead wasp corpses when you have figs, don’t be. Most modern cultivated figs are self-fertile, which means that they don’t rely on wasps to produce fruit. In those that aren’t, though, wasps are required for fruit production … and some of the crunchy bits aren’t seeds.
Gall Wasps (Family Cynipidae)
Oak Gall, Image by sakichin
Another really weird wasp/plant interaction occurs in the gall wasps. Like many other wasp species, the larvae of gall wasps are parasites, but instead of relying on animals, these wasps parasitize plants. When a female wasp lays her egg in a developing oak leaf, she will co-opt the entire developmental program of the leaf, causing it to produce a novel structure that’s ideally suited to provision and protect her developing young. Humans have had a long relationship with these wasps; for example, before the modern age, oak galls were used to create blue and black inks.
Ichneumon Wasps (Family Ichneumonidae)
Rhysaa persuasoria, Image by Oliver C. Wright
Ichneumon wasps are one of the most diverse families of parasitic wasp in the world. Most of the previous parasitic families that I’ve discussed have been koinobiont, which is to say that the adults paralyze their prey permanently, before laying an external egg; the larva will then eat its host, which has been essentially ‘frozen.’
Many ichneumon wasps, however, have a different parasitic strategy — they are idiobiont parasitoids. In the case of an idiobiont parasitoid, the adult wasp will only temporarily paralyze her prey while laying eggs, or may not paralyze the host at all. When she lays eggs, she does not lay them on the outside of the host, but generally lays them directly inside the host’s body cavity, and the larvae will hatch out and start to develop inside the hemolymph of their host — who will still be able to move, eat and grow, with the parasitic larvae inside. As the larvae develop, they will eventually begin to eat into the essential organs of their host. At this point, they will burrow out of the host.
In the case of some ichneumon wasps, the horror doesn’t even stop there! For example, some moth caterpillar parasites will hijack their host’s natural instinct to spin a protective cocoon for itself, and their hosts will instead spin a protective cocoon over the newly-emerged wasps, so that they can pupate … safe from OTHER parastic wasps.
This seems like a pretty awful deal for the host. (In fact, Darwin once said “I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of Caterpillars.”) However, these are one of the most important checks we have on pest species that attack our crops and other important plants. Because these wasps must be so well adapted to fight off the immune systems of their hosts (some even have symbiotic relationships with viruses that help them do this), most ichneumon wasps are very, very host-specific. Which means that if an introduced pest is destroying an important cash crop, you can generally confidently introduce its ichneumon parasites to control it, confident that these animals will attack only the species that is damaging. Parasitoid biocontrol can be very effective for this reason, and has distinct advantages over herbicides (which can threaten human health and target non host species) or the introduction of generalist predators (which can run amok in an ecosystem, targeting everything EXCEPT the intended host).
True Wasps (Family Vespidae)
Polistes exclamans, Image by A. Jaszlics
Okay, so maybe I have convinced you that most wasps are cool, but I have, so far, failed to address the species of wasps that most people think of when they hear the word ‘wasp.’ The ones that build giant nests, and live in huge colonies, and sting you when you get too close.
Well, saving the best for last, let’s talk about vespids.
The vespids are a diverse group of wasps that are found across the globe; the most familiar ones are the paper wasps in the genus Polistes as well as the hornets and yellow jackets. The reason that these wasps are so frightening is because unlike most other wasps, they don’t just use their stingers to subdue prey (and lay eggs), but instead spend a lot of time actively defending their nest sites by attacking and stinging animals that they see as threatening. Depending on the species, they have different thresholds of ‘threatening.’ Paper wasps, for example, tend not to care about large mammals hanging around close to their nests, unless those nests are physically disturbed, while hornets tend to actively chase people away from their nest sites.
These wasps are also some of our most important insect predators. Generally speaking, worker wasps spend much of their active time foraging, especially for caterpillars, which they kill and bring to their nests. These wasps will chew up their prey and feed it to the developing grubs (look, ma, no parasitism!), and the grubs in turn, secrete sugary substances for the adults to eat (the adults will supplement their diet with things like sugar and rotting fruit, which is why they are so attracted to your soda in summer).
The really, really cool thing about vespid wasps, though, is that they are one of the best systems we have for understanding how and why social behavior evolves. The family Vespidae includes animals that are totally solitary (potter and pollen wasps), and almost every level of social organization in between, from cooperative nest building to a hierarchical colony structure with only one laying queen. In many species of wasps, we can observe social structures where individuals cheat the system — for example, workers laying eggs instead of queens — and that allows us to observe these animals and ask really interesting questions about how social behavior might have evolved, and who benefits. Furthermore, we see some really crazy, innovative patterns in these wasps that we don’t necessarily find in other social insects — the paper wasp Polistes fuscatus has a strict system of social hierarchy within the nest, and because of it, these wasps have evolved the ability to recognize each others’ faces.
Fossil Wasp (Palaeovespa florissantia), Florissant Formation, Image from The Geological Society of America
Wasps have been around a lot longer than we have. In that time, they have become some of the most important animals in terrestrial ecosystems. Without wasps, our world would be a very different, and far less beautiful place.
You don’t have to love them. But please, give them at least a little respect.