The Rocky Egg Mass Picture Show

Aquatic insect egg masses are beautiful and important indicators of stream health.  Graduate student, Samantha Jordt, measures the health of restored vs. natural streams across North Carolina by recording egg mass abundance, and we wanted to share these egg-stream-ly beautiful globs and blobs!

“Aquatic insect eggs and their masses are incredible and diverse structures. They can be a riot of yellow dots cemented to the underside of a rock in a rapidly flowing river, like the psephenid or little white specks, suspended in a gelatinous matrix secured to a rock like the some midges or caddisflies. Other caddisfly masses are pale purple and laid in a purposeful and captivating fanlike pattern attached directly to the rock,” says Jordt. “These egg masses can contain anywhere from a few dozen to a few hundred eggs and are the future of a healthy, diverse stream.”

(All descriptions and pictures provided by Samantha)
These tombstone shaped masses are laid by female mayflies in the family Baetidae. Their eggs are so tiny and so closely packed that you might never know that that light-colored spot on a rock was actually hundreds of eggs unless you knew what you were looking for. In this photo, a female is in the middle of laying, she has landed on a rock and crawled to the underside before I rudely interrupted her and upended her nursery. These masses are found throughout the summer in North Carolina streams.
These pale pink egg masses belong to a group of caddisflies called the microcaddisflies or Hydroptilidae. They are called microcaddisfies because they are… tiny, often only 2 to 6 millimeters in length. It’s not surprising then that tiny caddisflies lay tiny eggs, .2-.3mm within masses no more than 5 mm in diameter.
(Above & Below) These blobs are the homes of dozens of little non-biting midge babies of the family Chironomidae. The eggs themselves are ovular and often see through so, with a microscope, you are able to watch these little guys wriggle around as they develop! Photographed are two different Chironomid masses, both like little boogers smeared on rocks. Other than the snotty consistency, the masses can be quite different from one another, for instance blob solo (above) is ~7mm in diameter while the others are much smaller (2-3mm). Midge eggs are found in streams all summer long though the types of masses boom and bust throughout the season.

(Above & Below) These bright yellow masses belong to the females of the water penny beetle, species Psephenus, P. herricki. The larvae look like little contact lenses with legs and can be found in fast flowing streams all year round, while the egg masses appear in the warm summer months. The adult female strolls around the stream bed until she finds a viable rock to lay on (pictured above).

Mystery Masses:

While the adult forms of aquatic insects are often charismatic (like caddisflies and dragonflies) their egg masses can often present a mystery.  Can you help us identify these mystery masses pictured below?  Tweet us if so!

This “mass” is about 2cm by 3cm. It was first recorded in July 15th and occasionally throughout the field season afterward. It always resembles a donut in that it is mostly circular with the middle devoid of mass. It is not clear if the mass is comprised of eggs; looking at a sample under a dissection scope yielded no clues other than it looked like the children’s toy “foam putty.”
This beautifully colored mass was seen only one field day at only one site. It is 7x10mm, the eggs ~.6mm.

Insects presence gives us a snap-shot of aquatic ecosystem health since they decompose leaf litter and support fishes.

Leave a Response

Your email address will not be published. All fields are required.