What is it about Bembidion heads? And, in particular, what is it with the heads of one subgroup of Bembidion, the Bembidion Series? The Bembidion Series is a large clade of few hundred species, and represents perhaps a quarter of known Bembidion (that’s a bit of a guess – I’d have to add up the numbers to be sure).
Most Bembidion have heads with the dorsal surface relatively flat and simple, with two shallow grooves just inside the eyes, like thus:
Within the Bembidion Series, some species have similar heads. Others have more complexly textured heads, including wrinkled ones:
But within the Bembidion Series there has evolved, at least 5 times, heads with converging, deep grooves on the head. Some of these are shown below.
Why are the heads like this, and only in this one group of Bembidion? Do they feed differently, or on different prey? Or does this have nothing to do with feeding, but instead is about burrowing? Or???