Colin Donihue

Alright, if you haven’t already taken the quiz, check out the previous post from Kat and see if you can guess the answers.

Here are a few pictures from Kat to distract you so you don’t see the answers ahead of time!

And now for the answers!

Were you able to recognize any of these major orders from just a single element? Here’s some more information about these orders and their diagnostic characteristics:

1. Hymenoptera (Formicidae): petioles

The order Hymenoptera includes bees, ants, and wasps. Ants, in the family Formicidae, are easily differentiated from other hymenopterans by the presence of nodes (either 1 or 2) on their petiole, which is the narrow connection between their thorax and abdomen. “Petiole” means “stalk” in Latin, and also refers to the skinny stem of a leaf. The petiole nodes of ants are hardened and tough to digest, so they often remain in lizards’ stomachs. Although ants provide minimal nutritional content, lizards will often eat them to fill up their stomachs (much in the same way I eat chocolate…).

2. Diptera: compound eyes

The compound eyes of flies are easily recognizable as thin domes covered with hundreds of dots. Each dot represents a single photoreceptor unit, referred to as an ommatidium. Each compound eye can have hundreds to thousands of ommatidia, and the two eyes on one individual may have slightly different numbers of ommatidia. Flies are not the only insects that have compound eyes, but their eyes can be distinguished by their size and general dome shape, as well as the presence of other clues within the stomach contents (e.g. short, triangular wings and fragile, often metallic abdomen exoskeletons). The ability of P. erhardii to catch dipterans demonstrates this species’ speed and dexterity: imagine trying to catch a fly with your mouth!

3. Coleoptera: elytra

The beetles are easily recognized by their elytra: the hardened forewings, which meet in a straight line down the abdomen and completely cover the hindwings when the beetle is not flying. Because the elytra are stiff and thick due to sclerotization, they don’t easily break down in the lizard’s gut. Although Coleoptera is the most diverse order of arthropods, I only find a few species of beetles in the lizard stomach contents. The lizards are restricted to eating smaller beetles that they are able to crush in their jaws or swallow whole.

4. Hemiptera: scutella

 Hemipterans are commonly referred to as “true bugs”, a vague term that is ultimately misleading, considering that the word “bug” means nothing in the field of entomology. The hemipterans are functionally diverse, including insects ranging from cicadas and stink bugs to leaf hoppers and aphids. My favorite hemiteran is the giant water bug (family Belostomatidae), which is known to prey upon frogs and even snakes. Hemipterans have a diagnostic triangular scutellum on their thorax, which can be seen in yellow in the microscope picture of stomach contents. Hemipterans are a favorite food source for P. erhardii: one lizard we caught had 38 hemipterans in its stomach!

The majority of the individuals in the stomach samples have come from these four orders, along with spiders and beetle larvae. However, I’ve found numerous other arthropods, as well as gastropods and plant material! I made a general key of the most common diagnosable elements I’ve found while analyzing stomach contents. If you’d like access to the key, or have any other questions about the diet preferences of P. erhardii, feel free to email me at kathryn.culhane@yale.edu!