Eye of the TIger Beetle

Larvae of tiger beetles make burrows in the soil, waiting in ambush for prey to approach nearby. The larvae use vision to detect their prey. However, beetle larvae contain only simple eyes called stemmata. Compound eyes only develop in adult beetles. How can tiger beetles “see” their prey?

Six Spotted Tiger Beetle, Cicindela sexguttata

Tiger beetle larvae have six stemmata, but only two have a role in detecting prey. The capabilities of the two prey-detecting stemmata are greatly expanded in tiger beetles compared to other insects. Expanding the number and quality of visual receptors in a stemmata requires expansion of the brain to process the signals. A region of the insect brain called the lobula plate typically remains undeveloped in larvae of insects with complete metamorphosis (including beetles). However, in tiger beetle larvae, the lobula plate precociously develops in the larvae and forms the larval tectum, an area unique to the brains of tiger beetle larvae. The tectum processes signals from visual receptors to locate and identify prey and trigger the attack response of the larva.

During metamorphosis to adult insects, the stemmata of the larvae degrade as do their connections to the nervous system. In tiger beetle metamorphosis, the stemmata degrade as does the tectum. The cells that in other beetles form the lobula plate have already been used by tiger beetles to form the larval tectum and are missing. Thus, the compound eyes of adult tiger beetles lack a lobula plate. In other insects, the lobula plate is associated with flight stabilization. We do not know how tiger beetle adults compensate for the absence of the lobula plate.