Walk Softly: Jaws vs The Fly

by Geoffrey Carpentier

In the last few columns, we explored the lives of some of the amphibians, reptiles, birds and mammals and how they catch and consume their prey. So now let’s focus on some smaller critters and see what techniques they utilize to capture and subdue prey.

In higher animals, mandibles refer to both the upper and lower jaw, but in insects, these structures refer to the lower part of the mouth only. Mandibles in insects are pairs of hardened structures that are used to grind, crush and chew food. They are then paired with maxillae to make them more efficient in feeding or defence.

Jaws are defined as “a pair of opposable articulated structures at the entrance of the mouth, typically used for grasping and manipulating food.” Arthropods (which include insects, spiders and crustaceans) have mandibles, which function to assist the animal to catch, hold and macerate prey so they can be consumed. In this discussion, I will focus only on insects, which have developed such that their mouth parts are greatly modified and look like fangs or pincers or any number of other structures that facilitate the feeding preferences of their host. Even within a species, the mandibles can vary greatly, such that a soldier ant can have formidable pincers to fend off intruders, and the other ants of the same species can have simpler mouth parts. Let’s look a bit more closely at some examples.

For the most part, insects have mouth parts designed to chew (e.g. grasshoppers), pierce/suck (e.g. mosquitoes), suck/siphon (e.g. butterflies and moths), or sponge (e.g. housefly). Even within the feeding techniques described above, what the animal eats may determine if modifications to the mouth parts are needed or not, even if the same feeding style is adopted. For example, an aphid might suck plant juices, while a female mosquito can suck blood, but the morphological adaptation of their mouth parts is very different between them, as the aphid’s mouth parts consist of stylets for piercing and sucking, while female mosquitoes have a proboscis adapted for piercing and sucking blood.

For carnivorous chewing insects, some will have mouth parts adapted to be serrated, pointed or knife-like to facilitate prey capture. For these insects, the chewing adaptation may be specific only to the larval (immature) stages, while the adults may adopt a different feeding style or perhaps not even feed at all! Caterpillars generally have broader, flatter mouth parts to grind up their plant-based foods, while the adults generally suck nectar. There are so many adaptations it’s hard to summarize them here, but one other interesting example of variation is that bees primarily use their mandibles to manipulate and shape wax, while many paper wasps have mandibles adapted to scraping and ingesting wood fibres.

Dragonflies and damselflies belong to the insect order Odonata, meaning “toothed jaw”. The mouth of a dragonfly (whether adult or immature) is a complex structure that consists of an upper lip (labrum) and a lower lip (labium). The labrum and labium function together to capture and secure prey while the jaws do the chewing. The jaws, which work from side to side, are made up of one pair of upper mandibles and two pairs of lower maxillae. These jaws sport a series of curved hooks to restrain prey, making them formidable predators!

Butterflies and moths generally do not pierce, lick or sponge their food, but rather probe it and, as such, have mouth parts adapted to sucking through a unique structure called a proboscis, which may be longer than the insect’s body. Finally, sponging insects, such as some flies, have a different strategy where they have unique structures that move the food through pseudotrachea to the esophagus by capillary action. The housefly can also eat solid food by secreting saliva and dabbing it over the food item. As the saliva dissolves the food, the solution is then drawn up into the mouth as a liquid.

So, there you have it. I hope you enjoyed this little journey into what strategies and morphological adaptations animals utilize to assist in prey capture and consumption. I know this one got a bit technical, but it is a fascinating study nonetheless.

Geoff Carpentier is a published author, expedition guide and environmental consultant. Visit Geoff on-line on LinkedIn, Facebook and Instagram.