Minimal Effort, Maximum Results: Yellow Pan Trapping for Ceraphronoidea

Yellow pan traps are an invaluable collection method for microhymenoptera. Popularized by Lubomír Masner, the trap consists of a yellow plastic bowl filled with water and a drop of soap. The purpose of the soap is to break the surface tension so that insects fall into the water and drown, allowing them to be collected.

As part of an outreach activity on collection methods, I put out 50 yellow pan traps in a flower garden near the Frost Entomology Museum. The traps were only out for four hours, between 1:30PM and 5:30PM, but even after such a short time we still captured a large amount of insects. There were wasps trying to land in the pan traps before I even filled them with water!

The flower garden outside of Head House II at Penn State, where I put down 50 yellow pan traps. Photo by Carolyn Trietsch (CC BY 2.0). Click for source.

When I sorted through the sample, I was shocked to find over 50 ceraphronoids from just a few hours of collecting. I found Ceraphron, Aphanogmus, and even one female Dendrocerus specimen, my first Megaspilidae of the month! I got more specimens in four hours of pan trapping than I did in a week of malaise trapping.

A lot of over 50 Ceraphronoidea captured in just four hours of yellow pan trapping. Photo by Carolyn Trietsch (CC BY 2.0). Click for source.

If you collect or study microhymenoptera, do not underestimate the value of yellow pan trapping! In this case, minimal effort yielded maximum results!

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Megaspilus armatus: smooth vs. rugose?

While imaging some Megaspilus armatus specimens, I noticed a unique difference in the front of the head between male and female specimens.

A female Megaspilus armatus specimen (identifier PSUC 86124), with an arrow pointing to the smooth area on the front of the head. Photo by Carolyn Trietsch (CC BY 2.0). Click for source.

While male specimens had rugose or rough sculpturing across the entire front of the head, female specimens had smooth areas. I checked several specimens and it was consistent across specimens from Canada and the USA.

The front of the head of a male Megaspilus armatus specimen (identifier PSUC 86236), with an arrow pointing to the same area as on the female specimen above. Photo by Carolyn Trietsch (CC BY 2.0). Click for source.

I’m not sure if this a secondary sex characteristic,  a by-product of genetics, or something more, but it is worth noting, especially since it is consistent for this species over a very large geographical distribution.

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Experts ask for help

There’s a misconception among non-scientists that an expert always knows the answer to a question.  While that’s often the case, especially when the question is related to an expert’s field of study, it’s also common that we don’t know the answer immediately but have an idea of where to find the information. Sometimes, even that fails and the expert needs to ask for help.

As the insect identifier for Penn State Entomology, I need to be able to recognize or identify many species of insects and other arthropods across a wide variety of groups. This is pretty different from most taxonomists and systematists, who focus on one particular group and study it intensely. However, even within my broad knowledge, there are certain groups that, for whatever reason, I’m not great at identifying. Some of those groups I haven’t been exposed to and given the right training or practice could probably identify to a useful level with relative ease. Most microhymenoptera, especially chalcidoid families and ichneumonoid subfamilies, fall into this category. Other groups I’m just not that interested in personally.

Eurytomidae are an example of chaldicoid wasps.
“Eurytomidae” by Vida Van Der Walt – own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

With a few exceptions, Lepidoptera, which are the moths and butterflies, is a group that I am generally terrible at sight identifying. I have to picture book (that is, break out a book full of photos or visit a website with photos) most adult moth identifications. I’m even worse with all but the most common caterpillars.

I recently received an identification request for an egg mass that was found on the bottom side of a trumpet vine leaf. The client was worried that the insects would destroy the vine when the hatched. I was pretty certain that the eggs were some kind of lepidopteran, but only had grainy photos to go on.

Eggs on trumpet vine.
Cheri Micale, Penn State.

The eggs hatched while the extension educator who processed the request had them, so I received additional images. Ah ha! It’s definitely some kind of caterpillar (or maybe sawfly).

Recently hatched caterpillars.
Cheri Micale, Penn State.

We’re getting closer, but it’s not enough for a positive identification. I requested the specimens with a plan to raise them as young caterpillars, especially 1st instar, are difficult to impossible to identify. Unfortunately, 1st instar caterpillars are fragile and they died in the mail, so my plan to raise them was foiled. What to do now? All of the field guides and resources available for caterpillar identification are focused on older caterpillars, and I’m not an expert in Lepidoptera who can recognize such young caterpillars. Fortunately, there is a community of professional and amateur experts who might be able to help on With that in mind, I took a stereomicrograph (a photo using a stereomicroscope) and uploaded it to the website in hopes that someone will be able to identify the caterpillars. I’m out of resources to do so myself and had to ask for help.

1st instar caterpillar collected on trumpet vine. Michael Skvarla, Penn State.


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Important Figures in the History of Natural History: Aristotle

This post is the first in a short blog series featuring important figures in the history of natural history.

Though he is often thought of as a biologist, Aristotle was actually interested in the study of the soul and the cosmos. At his time, it was thought that celestial bodies on the heavenly plane (i.e. stars) were perfect, and that organisms on the terrestrial plane were imperfect imitations of these perfect heavenly bodies. Aristotle wanted to study the stars but could not observe them except at a distance; because he could not study the stars, he chose to study animals instead.

One of his most famous works is the History of Animals. Aristotle believed that everything on the terrestrial plane was composed of the 4 elements: earth, wind, fire and air. As a result, the History of Animals is full of descriptions and classifications of animals as “hot”, “cold”, “wet” or “dry”; this is related to their elemental composition, as in how much “earth” or “wind” is in the animal. Though it may seem odd today, Aristotle’s way of thinking set the foundation of how the natural world was studied for hundreds of years.

Aristotle studied sexual reproduction in depth, especially in domesticated animals and humans, but he believed smaller animals, including insects, were the product of spontaneous generation. He wrote of the “king” honey bee in hives and observed bee larvae, but he believed that honey bees gathered their larvae from flowers and brought them back to the hive to care for them. He was not aware of pollination, and believed that bees gathered honey from the air, where it occurred in droplets so small that only bees were able to collect them.

Raphael’s “The School of Athens”, showing Aristotle on the right, walking next to his teacher Plato. Photo by NASA Blueshift (CC BY 2.0). Click for source.

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Collembola on the tides

After driving up to Maine for a friend’s wedding, we decided to take some time to explore the coast. We stopped at Wolfe’s Neck Woods State Park, where we found the following cluster of insects floating on the surface of a tidal pool.

A raft of Collembola found in a tidal pool. Photo by Carolyn Trietsch (CC BY 2.0). Click for source.

These are Collembola or springtails. According to Frans Janssens, laboratory associate of the Department of Biology at the University of Antwerp, Belgium, this species is likely Anurida maritima (Neanuridae: Pseudachorutinae), a common intertidal species.

This species can commonly be found on the surface of the water in littoral or intertidal zones, forming rafts like the one pictured above. These Collembola are scavengers, but likely feed on diatoms and other plankton in the water as well.

According to Frans Janssens, the rafting behavior is a “side-effect of the meniscus that is formed by the water surface film”. When Collembola aggregate and float together, they create a depression or “pit” in the surface of the water. The more Collembola that gather, the deeper this pit in the water’s surface becomes, and the harder it is for them to get away from the rest of the group. However, this is not necessarily a problem; being part of such a large aggregation could offer a valuable opportunity to find mates and breed.

The rafting behavior could also serve as a means of dispersal. The tides and current could carry clusters of Collembola up and down the coast, or even to oceanic islands (Hawes et al 2008). This rafting behavior may have allowed Collembola to reach and colonize the Galapagos Islands (Coulson et al 2002).

Check out a video of this cluster of Collembola below!


Coulson, S. J., Hodkinson, I. D., Webb, N. R., & Harrison, J. A. (2002). Survival of terrestrial soil‐dwelling arthropods on and in seawater: implications for trans‐oceanic dispersal. Functional Ecology, 16(3), 353-356.

Hawes, T. C., Worland, M. R., Bale, J. S., & Convey, P. (2008). Rafting in Antarctic collembola. Journal of Zoology, 274(1), 44-50.

Special thanks to Frans Janssens for his help and expertise!

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