Niche Insects: Discovering Life Under Rocks

Most people hiking in Glen Park pass by rocks without pausing to flip them over and photograph what may be living underneath. Many people who are hiking there are birders - looking up above at Red Tailed Hawks or listening to the calls of Great Horned Owls. Some people are simply enjoying the scenery for no particular reason.

But when I visit O'Shaughnessy Reservoir, a relatively undisturbed patch of scrubland next to Glen Park, you'll often find me flipping over rocks in the grass in search of wildlife-from tiny springtails and beetles to larger alligator lizards.

Exploring the scrubland at O'Shaughnessy Reservoir!

Why pay attention to small animals?

Why is it important to search for these small animals, you might ask? Despite their size, these often-overlooked creatures play a vital role in the ecosystem. They pollinate plants, recycle nutrients by breaking down dead organic matter, provide food for larger organisms, and serve as indicators of environmental health. By studying and appreciating them, we can gain a better understanding of how ecosystems function and why protecting even the smallest organisms is important.

Why do you like doing it?

I think it's less about liking flipping rocks; it's more about engaging with nature and finding something that can contribute to the scientific community. Even small animals can tell you a lot about how the ecosystem is working, and I enjoy noticing things most people walk past. It also feels rewarding when I find something new or unexpected in an area I haven’t explored before.

How do we know that an area has a high likelihood of finding a species?

Over time, I've learned that some parts of the park experience less disturbance than others. Areas I haven't searched in a long time are the most rewarding because their microhabitats have had time to recover. In these spots, I'm more likely to find small, animals that I haven't found before.

I tend to search for animals under rocks in the exposed grassland area. Since the surface of the rocks match the color of the animals, it often takes me a while to locate them on the rock.

How do you make sure you're not disturbing the habitat by flipping?

The scrub ecosystem, despite its harsh appearance, is surprisingly delicate. Every time I flip over a rock, I temporarily disturb the habitat of the animals living beneath it. To minimize my impact, I avoid searching the same area repeatedly. Instead, I rotate between different rocks, bushes, and boulders, giving each microhabitat time to recover. Each rock creates slightly different conditions - varying in moisture, temperature, and shade. Exploring new areas not only reduces human impact but also increases the chance of discovering different species.

What kinds of animals do you find?

The organisms I most likely come across are arthropods. Arthropods are a huge group of animals; 80% of all known animal species fall within Arthropoda. Within the 33 acre park itself I have found around 90 species of unique arthropod species, most of them being beetles, spiders and ants.

I am also fond of reptiles. I have found 3 species of snakes and lizard at this park out of 6 species that are native to San Francisco proper.

What's you're favorite group to observe, and what's you're all time favorite organism?

The first question is tough! In terms of species diversity, I would say ants or beetles.

Most of the time when I'm in an urban area I see invasive ants like Argentine ants (Linepithema humile). But when I'm in the field just a couple blocks away from home, there is much more ant diversity. While Argentine ants are still present, they are often replaced by native ones like Monomorium ergatogyna, Camponotus vicinus and Pheidole pilifera, which I just found a couple days ago!

Native Pheidole ants (big-headed ants) found at the park. These are thought to be P. californica although more specific examination is needed for proof

I also enjoy finding beetles. Beetle groups are so diverse in terms of morphological variation in body structure, including differences in exoskeleton form and elytra (wing cases), and overall proportions. I'll often approach beetles thinking I’m seeing the same species repeatedly, but when they’re identified, I realize they’re actually entirely different species.

This extremely tiny beetle Apocrypha cf. anthicoides was found under a rock at the park. It took me a while to spot this beetle because of its miniscule size and it's camouflage

My all time favorite specimen, however, has got to be this Phidippus johnsoni, or the Johnson's jumping spider. It is a very goofy looking spider with fuzzy pedipalps and a fuzzy red abdomen. They are only about a cm long and very flighty so they easily get missed by hikers and regular people.

goofy ahh spider