What eats butterflies (and moths!)

Butterflies and moths (Lepidoptera) form a vital part of the food chain. Most are herbivorous and they provide nourishment for predators from tiny insects to… man. Within this range there is a huge spectrum of predation going on, as well as an arms race with plants and predators that started over 60 million years ago, and is still on the go.

It’s actually a good thing that insect predation rates are so high because they typically lay from dozens to hundreds of eggs, and Lepidoptera are no different. To maintain numbers, each coupling only needs to produce two offspring – if it were not for predators, we’d be buried in insects!

One could easily write a book on Lepidoptera predators because there are so many. All we can do here is go through the categories, give some examples and use some of these to illustrate interesting points about predation. So here goes, from the smallest to the biggest…

Actually, the smallest predators are microbes. Viruses, bacteria and fungi all take their toll. We see these having an effect most often when we rear Lepidoptera larvae in captivity, because overcrowding and food that’s past its best can make larvae more prone to disease. But, there are some very interesting things happening here. Those of you who’ve watched Sir David Attenborough’s Planet Earth series may remember the caterpillar-killing Cordyceps fungus, whose mycelium invades insects’ bodies before putting out fruiting bodies. The mycelium is known to influence behaviour; infected individuals may crawl into places that offer an advantage to the fungus when releasing its spores.

Lots of insects eat Lepidoptera. These fall into two categories. Parasitoids lay eggs inside the eggs, larvae or pupae of Lepidoptera. These then hatch into larvae which eat the victim alive from the inside. There are tiny wasps (Hymenoptera – Braconidae) that hitch a lift on a butterfly’s abdomen, and pop an egg into each egg the butterfly lays. Or they may inject eggs directly into the larva, or pupa. These little creatures are seriously weird and creepy! Most are infected with a special virus which suppresses the host’s immune system and thus protects the wasp’s grubs from it. Some exhibit ‘polyembryony’, in which one fertilised egg undergoes cell division as do all eggs – but at some stage, each divided cell splits up into a separate grub embryo. In such cases, several individual wasps result, all of which are identical ‘twins’. In some species, the embryos differentiate into two types. One becomes an adult wasp; others become ‘precocious larvae’ which roam around the host’s body, eating any other parasitoid larvae they encounter.

Others (Ichneumonidae) usually have one large grub, which becomes a single adult. The grub bursts from the fully grown larva, or pupa, of the Lepidopteran, then spins an elaborate cocoon close to its victim’s corpse.

Other parasitoids are flies (Diptera), usually of the family Tachinidae. The mother fly lays an egg either on the larva, which then hatches and bores through the skin, or in some cases, a freshly hatched maggot. Others lay eggs on leaves the Lepidopteran larvae eat, and are ingested with food.

Hyperparasitoidism exists, where wasps lay eggs inside parasitoid grubs living inside a caterpillar.

The end result is usually the death of the larva. A healthy looking caterpillar suddenly becomes moribund, and one or more grubs bore through its skin, and spin cocoons next to its corpse. Occasionally it will survive this and keep feeding, but this is rare. Or, the lepidopteran pupa may form, only for a grub to bite its way out and pupate nearby. And in some species, the parasitoid pupates inside the host and the adult comes out.

In some egg parasitoids, microscopic wasps emerge from a lepidopteran egg – sometimes dozens from one egg. If you are squirming as you read this, you are not alone – HR Giger got his ideas for the face-hugging Alien in the movies from these insects! We use the word ‘parasitoid’ instead of ‘parasite’ because the latter don’t kill their hosts…

Lepidoptera have developed some defence mechanisms against parasitoids. Some simply drop off their host plant as soon as they sense the touch of another insect. But one of the most fascinating ways they avoid parasitoids is to engage other insects as bodyguards. Most of the butterfly family Lycaenidae (blues, coppers, hairstreaks etc) have larvae that associate with ants in some way. The ants swarm over the larvae, discouraging parasitoids from attacking them. The association ranges from simply giving off chemicals that attract ants whilst feeding on the host plant, to living inside ants’ nests and coming out to feed, often at night only. Others are fed by the ants like baby cuckoos, or have evolved to feed off the ants’ young, becoming carnivorous parasitoids themselves…

Of course there are many insects that simply catch and kill lepidoptera or their larvae. Caterpillars are actively hunted by certain wasps. Some wasps sting them to paralyse them, before sealing them into a cell in their nests. This is similar to parasitoidism, because the wasp grub eats the larva alive, leaving the vital bits till last. Other wasps butcher their prey before feeding their larvae.

Carnivorous ants like the genus Anaplolepis (Pugnacious Ants, Hymenoptera – Formicidae) also catch larvae, and drag them into their nests to be consumed.

Many insects prey on adult butterflies and moths. Mantids (Mantodea – Mantidae) lurk balefully on flowers and catch them as they suck nectar.

Male Hanging (or Scorpion) flies (Mecoptera – Bittacidae) are another example of insect weirdness. Males catch butterflies and dangle them from their legs, as a nuptial gift to a female. The female then eats the butterfly whilst mating.

Robber Flies (Asilidae), like Dragonflies and Damselflies (Odonata) are the hunters of the insect world. Odonata seem to be non-specialists, but Asilid flies seem to prefer Lepidoptera. They seem to know when a colonial, short flight period butterfly is having a hatch, and hang around. They inject saliva carrying very strong proteolytic (protein destroying) enzymes, instantly killing their prey, whose innards turn into a soup that the fly can suck up.

Odonata, like Mantids, chew their prey up. I told you this article was not for the squeamish!

And besides other insects, Lepidoptera have another group of arthropods to contend with – Spiders (Arachnida). There are thousands of species of spider, and their hunting strategies vary. Some roam around and leap on their prey, like the Wolf Spiders (Lycosidae) or Jumping Spiders (Salticidae). Others lurk on flowers, even adopting the same colour as a flower – to the disadvantage of nectaring Lepidoptera, like the Flower Crab Spiders (Thomisidae). And of course there are the many web-spinning spiders, into whose traps many Lepidoptera fly.

That’s just a selection of invertebrate predators that Lepidoptera have to contend with. We still have to consider the vertebrates!

Lizards, and other reptiles such as chameleons, and amphibians – frogs and toads – are major predators. And of course birds, many of which specialise in eating all stages of Lepidoptera. Moths are eaten in huge numbers by bats. It’s here where the chemical warfare comes in.

Butterfly and moth larvae most often eat plants, and we know that plants, over time, have developed chemical defences to deter herbivores. This doesn’t only go for Lepidoptera – even antelope are deterred by bitter tasting plant compounds. And over time, Lepidopteran larvae developed the ability to digest (metabolise) these toxic and nasty tasting chemicals. As a result, many became toxic and nasty tasting themselves! There is evidence that this led to the development of warning colours and patterns. Such advertisements only work on predators who hunt by sight – so diurnal behaviour (day flying) led to the evolution of butterflies themselves. But, we now know that some moths can hear bats’ echolocation calls, and send out a sound signal that says ‘I taste nasty – eat me at your peril’!

As well as warning colouration, another defence against predators that hunt by sight, is to have wing patterns that act as a shock tactic or a deterrent. Many butterflies and moths have prominent eyespots on their wings, which may fool lizards and birds into thinking they have disturbed a creature that might threaten them. And some have tails on their hind wings, often combined with an eyespot, which fools predators into aiming at the ‘wrong end’ of the butterfly.

Caterpillars also defend themselves by sporting eyespots – and many are spiny and look very unappetizing. Not to mention the many species whose hairs are irritating to the touch, or even stinging.

These defences are not foolproof, and many butterflies whose larvae eat toxic plants (or which ingest toxins as adults) fall prey to vertebrate, as well as invertebrate, predators. The latter don’t seem to be affected, as shown by the picture of a Flower Mantid devouring a Blood-red Acraea. Some vertebrates are affected. Early work on bird predation showed that Blue Jays (an American study) vomited when fed Monarch (Danainae) butterflies, and learned to avoid them. A famous Lepidopterist, Torben B Larsen, had a pet chameleon, Cleopatra, whom he fed butterflies. Feeding her a Bitter Acraea made her turn black and refuse to be handled for some time!

Many insectivorous birds, such as White-eyes, Thrushes and warblers, specialize in hunting larvae. Seed-eating birds such as Weavers feed protein-rich caterpillars to their young in the nest. But the birds that eat adult Lepidoptera the most seem to be Bee-eaters. Perhaps because their insect-hawking exploits are highly visible and hence photographed often by birders, they are familiar butterfly eaters. But they seem to be happy to catch and eat butterflies with warning colouration, such as Bitter Acraeas. Indeed, some birds, such as Cuckoos, seem to specialize in eating Bitter Acraea larvae – which are often full of bitter tasting toxins, even cyanides!

Then we come to mammals. Monkeys love to eat caterpillars – I have often lost Strelitzia Nightfighter larvae to a troop of Vervets, but haven’t been able to photograph them eating them. I’ve seen my cats and dogs catch and eat moths and butterflies that I’ve reared and released. Mice and rats eat caterpillars, pupae and moths that have been attracted to lights and are resting in the open. Bats are major predators on nocturnal moths, to the extent where moth populations close to brightly lit buildings are under threat. It’s been shown that the bat populations close to large sports stadia such as Moses Mabhida, have swung away from fruit-eating species to insectivores.

Man is a mammalian predator of Lepidoptera. There is a big ‘Ewww’ factor against eating insects, but we’ve all heard of the Mopane Worm, which is the larva of a big Emperor moth, Gonimbrasia belina. It’s not the only Emperor moth that gets eaten – these fat, juicy caterpillars are popular ‘bush food’, even the ones that look unpalatable, like the black, orange and red Common Emperor, Bunaea alcinoe.