Invertebrates
Peanut-head Bug
Fulgora laternaria · also called peanut-head bug, lantern fly, machaca, alligator bug
The peanut-head bug is a large tropical planthopper with a growth on the front of its head that really does look like an unshelled peanut — and, on closer inspection, like the face of a small lizard, complete with fake eyes and teeth. It is entirely harmless, a sap-drinker with no bite at all, but it carries one of the most colourful pieces of folklore attached to any insect.
Overview
The peanut-head bug lives on the trunks of large trees in the rainforests of Central and South America. It is about 8.5–9 cm long including the wings, mottled greenish-brown, with a hollow, peanut-shaped projection at the front of the head. It feeds only on tree sap.
Three layers of bluff
The head projection is marked with fake reptile eyes, nostrils, and teeth, so a predator that gets close to the bug’s real, vulnerable front end sees what looks like a lizard face. If that fails, the bug snaps open its hindwings to flash a pair of large eyespots. And as a last resort it releases a foul, skunk-like chemical.
The lantern-fly myth
Despite the name, the head does not glow. The idea came from early descriptions and illustrations and stuck to the whole planthopper group, though no planthopper is known to be luminous.
A deadly reputation it does not deserve
In parts of Latin America the machaca is feared, with a belief that its bite kills within a day unless the victim has sex. In reality its mouthparts can only pierce bark; it cannot bite a person at all.
Status
The peanut-head bug has not been assessed. It is widespread and locally common but depends on intact forest.
Peanut-head Bug: common questions
Does the peanut-head bug's head really glow?
No. The name lantern fly, and the older belief that the bulbous head is luminous, seem to have come from seventeenth and eighteenth-century accounts and illustrations of the insect, and once the idea was in print it spread to the whole planthopper group. Careful study has never found any light-producing organ or any glow in the peanut-head bug or its relatives. The head projection is a hollow, lightweight structure whose job is visual mimicry in daylight, not illumination, and calling the animal a lantern fly is now recognised as a historical error that has simply proved impossible to shake off.
What is the peanut-shaped head for?
It is a decoy. The projection is hollow and adds little weight, and its surface is marked with a pattern of false eyes, a false mouth, and false teeth arranged to look like the head of a small lizard or snake. A bird or lizard approaching the bug from the front, which is where the real, vulnerable head and body are, is confronted with what looks like a reptile face, and may hesitate or break off the attack. It is one of several layered defences the bug uses, the others being the wing eyespots and the smelly chemical spray.
Is the peanut-head bug dangerous or venomous?
Not at all. It has no venom, no sting, and no ability to bite a person. Its mouthparts are a set of fine, needle-like stylets bundled together, designed solely for sliding into plant tissue and sucking sap, and they cannot penetrate skin or deliver anything harmful. The elaborate folklore that surrounds the machaca, in which its bite is said to be fatal unless the victim quickly finds a sexual partner, has no basis in the animal's biology and appears to be a piece of rural humour that took on a life of its own.
Where and how would you see one?
Peanut-head bugs live on the trunks of large trees in Central and South American rainforest, where their mottled brown-green colouring makes them very hard to spot against bark, especially as they tend to sit still by day. They are most often found by guides and naturalists who know which trees to check and look for the distinctive silhouette of the head. Disturbing one usually triggers the wing-eyespot display and then, if pressed, the chemical spray, after which it may make a short, clumsy flight to another trunk.