Why do cockchafers have feathery antennae?

Cockchafers (or Maybugs) are coming to lit windows near you. Look out for their distinctive, fan-shaped antennae.

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Cockchafer

Cockchafers, along with stag beetles, dung beetles, dor beetles and scarabs, have the last three to seven segments of their antennae expanded into flat, plate-like leaves, which sit in a distinctive fan-like arrangement.

Antennae are the olfactory sense organs of insects, and this formation greatly increases the surface area available for the chemosensors.

Insects usually need to sniff out two things – food sources and mates.

In dung beetles, male and female antennae are very similar, suggesting that both are attracted to faecal odours, so can locate a mate at a pat.

Male and female cockchafers may use some subtle chemical signal from decay, or particular roots, to co-ordinate a rendezvous, but the fact that males have seven club segments and females only six suggests that males also respond to female pheromone scents. 

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