On May 26th 2012, this click beetle began laying her eggs on a log along the Orange trail of the State Botanical Garden of Georgia in Athens, GA. These beetles are quite noticeable due to their large size and distinctive eye patterns on their pronotum. At the beginning of the video (while she is stationary), you can see some very tiny red mites walking across her body.
She wondered around on a downed tree and assessed possible egg laying sites. She frequently probed suitability using her ovipositor. She then oviposited at the base of a tree fungus known as red rot (Dichomitus squalens). This observation has been registered in iNaturalist.org.
The family Elateridae is commonly called click beetles, elaters, snapping beetles, spring beetles or “skipjacks”. There are about 9300 known species of click beetles worldwide. Most species are brown to black in color, although some have reddish and yellowish colors and patterns.
The Eyed Click bug (Alaus oculatus) is the largest among the wood-eating elaterid wire-worms. Their grubs are not borers. Grubs penetrate wood after it starts to decay and become soft.
They feed on other insect larvae living under the close surface of the bark.
Up until recently, the research focused on the most striking adaptation: The eyespot pattern. This grey/black speckled insect carries a pair of visually striking eye patterns covering one third the length of the pronotum. False eyes have evolved independently in moths, cockroaches and mantises, butterflies and beetles. In most insects false eyes serve a “lose-little-to-save-much” type defense strategy. However in this bug the super black eyespots serve for intimidating predators. The visual deterrence may provide protection to vital organs in the thorax such as the dorsal vessel and thoracic ganglia.
Stiff bristle-like hairy surface structures called setae trap light leading to near complete absorption with a super black appearance. Well known in the natural world from bird feathers and butterfly scales, the super black phenotype has evolved independently many times. The optical industry is quite interested in the eye pattern for its exceptional ability to reduce specular reflection. The eyespots form from a perpendicular array of setae with black pigmentation. Each eyespot is circled by a ring of flat clear setae that form the white “eyeliner”. The black eyespot absorbs ten-fold more light than the eyeliner thanks to the interplay of structural and pigmentary absorption. The intense black of the eyespot provides a stark contrast versus the eyeliner making the insect immediately noticeable to a predator as an aposematic signal. The eyespots may startle enemies with the illusion of a formidable opponent.
The shape of the pronotum might also have evolved to avoid spider attacks. One individual observed in Germany was recorded as it escaped from a spider web by slipping out of the tight knit fiber spun around its pronotum:
click beetle vs. daddy longlegs from Pascal Schneider on Vimeo.
Here we see a female in search of an egg-laying site. She inspects cracks and bases of fungi on a decaying log using her ovipositor. After mating, females shift to behaviors that help the survival of offspring. The behavioral switch is kick-started by a small male protein called Sex Peptide (SP), transferred to the female in the sperm. SP rapidly renders females unreceptive before the next day.
Oviposition is an important event in the insect life cycle. Larvae have limited ability to change their locations. The site choice of the female for egg-laying has a fitness consequence. Females actively search for places that will protect eggs and larvae from desiccation, predators and pathogens and subsequently provide feeding opportunities. The female is guided through a neural circuitry for when, where and how to place an egg. This circuitry is turned on rapidly within minutes or hours after mating. The Sex Peptide Receptor (SPR) is identified as a G protein-coupled receptor that mediates activation of reproductive tract sensory neurons. Egg-laying behavior is reinforced by joint action of the hormone Ecdysteroid and sex-specific transcription factors Fruitless (FRU) and Doublesex (DSX). The circadian rhythm also has a large role in oviposition.
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