Insects work hard to get their liquid-only meals

The tiger swallowtail butterfly uses a straw-like drinking tube known as a proboscis to sip nectar.

Lisa Timpf

Advocate Contributor

With snow and ice piling up, many Norfolk residents are looking forward to springtime.

Attendees at the Norfolk Field Naturalists’ February 11 speaker event had a chance to dream about warmer days as Dr. Brent Sinclair spoke about insects that are much more likely to appear once the snow has vanished.

Sinclair, a Professor in Cornell University’s Department of Entomology, discussed the challenges posed for insects who live on a liquid diet. He also explained some of the ways they overcome those difficulties.

Some insects that rely on liquid diets are ones we admire. Butterflies, for example, are visually appealing and also play a role in pollination. Aphids, leafhoppers, and mosquitos, on the other hand, are less well-liked. Whether seen as friend or foe, as Sinclair’s talk pointed out, insects whose diet is liquid-only can do some remarkable things.

These insects need to take in a lot of liquid to get the nutrients they need. Some must consume many times their body weight. Aphids, for example, drink eight to 32 times their own body weight per day.

This means liquid-diet-reliant insects must be good at separating out water from the nutrients they want to keep. Many insects have a complex arrangement of Malpighian tubules to process liquids.

Obtaining the liquids in the first place isn’t always easy. Butterflies use a straw-like device called a proboscis to drink nectar from flowers. Aphids, which dine on phloem sap, bite the plant, then drink the sap as it is pushed out. Insects that live on sap from the plant’s xylem have developed other methods to extract the fluid they need.

Among the insects drinking from the plant’s xylem are leafhoppers, froghoppers, and spittlebugs. Phloem sap, the aphids’ food source of choice, is under positive pressure, which means aphids merely have to bite into the plant at the right place and sap will flow. Xylem sap, on the other hand, is under negative pressure, which creates challenges. 

Froghoppers have overcome this issue by developing a specialized muscular structure known as a cibarial pump, which allows them to create the equivalent of over 100 vacuum cleaners’ worth of suction. 

When mosquitos drink our blood, they run across a different problem. Mosquitos are cold-blooded, which means they rely on outside temperatures to control their body temperature. Human blood is at around 37 degrees Celsius. Drinking blood could potentially heat the mosquito up so much that it causes biochemical damage. To counter this, mosquitos have developed “heat shock” proteins to minimize the impact.

Sinclair showed a video that demonstrates another remarkable feature about mosquitos. It may appear, watching one in action, that mosquitos just jab you and start drinking. But in the video, which showed the mosquito’s mouthparts under a microscope, observers could see the insect moving its stylus through body tissues with incredible precision to get to a capillary carrying blood. Only then did it start to enjoy its meal.

Sinclair’s talk provided a new appreciation for how hard insects that live on liquid diets have to work to get their meals. Even if it doesn’t make us feel more charitable towards aphids, leafhoppers and mosquitos, at least we can look at the insects that share our yards with a new appreciation for their marvelous complexity.