Читать книгу Extreme Insects - Richard Jones - Страница 14

NAME	European snail beetle Drilus flavescens
LOCATION	mainland Europe and the UK
ATTRIBUTE	most extreme difference between male and female

Males and females are different. Males produce huge amounts of tiny sperm, which they generally try to spread about between as many females as they can. Females carry the eggs, and although they may benefit from males competing for their attentions, multiple matings carry a cost in terms of time wasted and sometimes even physical damage. These different biological drives often produce very different behaviours in male and female of the same species, and sometimes also different body forms. In most insects these structural differences are small, but in one group of beetles, males and females are so different that they look like completely different organisms.

The European snail beetle, Drilus flavescens, is small (4 to 7 mm) and brown; it has a black head and thorax, and feathery antennae – at least the male has. The female, by extreme contrast, is a large, soft, flabby, caterpillar-like creature, 50 times as large as the male. The males fly on hot sunny days, but the females lack both the normal hard beetle wingcases and also the functional membranous flight wings. The distribution of the males shows that the species is fairly widespread on limestone or chalk soils, but despite this the female is virtually unknown. In fact, the female of this peculiar species is so rarely seen that there was no reliable published picture of her until this mating pair was photographed in 2003.

The larvae of Drilus eat small snails. Despite being a widespread insect, the rarity (or perhaps the secretiveness) of the females and larvae meant that the beetle’s life cycle was not worked out until 1903. Quite why males and females of Drilus should be so very different is still a bit of a mystery, although many female glow-worms (also beetles but in a completely different family) are also wingless, and their larvae, too, are snail predators.