Syrphid migration

Some flies migrate, just like some birds and butterflies, but it is rarely recorded. In fact, this might be the first record of a flower fly (or hover fly) migration for North America!

It took place on April 20th, 2017, at beautiful Montana de Oro State Park. I was walking with my dear friends Marianne and Gary Wallace  when Gary said “look at all those bees!” I looked, and realized that they were not bees, but flower flies, thousands of them. They were flying against the wind, in a northward direction, not stopping at all. I actually got some video of this migration; have a look.



The flies look like bullets going by. We didn’t have any collecting gear (duh, it’s a park), but we tried knocking some down, to no avail. They were moving fast and avoiding contact. I tried taking some stills, and this is my best (bad) photo:

Why would syrphids migrate? These flies feed on aphids as larvae, and aphids are found on tender new growth. California’s rainfall comes during a short time in the winter, and then things dry up. An hypothesis is that as the more southerly vegatation dies off from lack of water (and thus also the aphid supply dwindles) the flies move northward looking for green, still tender fields, well stocked with their aphid food.

This was something I never expected to see, but wanted to record so others could keep their eyes open for it in the future. I’ll be back next year looking for them at the same time of the year, hopefully to learn which species they are.

In Costa Rica with bloodsuckers

Being in the field, it is hard to ignore the biting flies. Mosquitoes, black flies, horse flies, sand flies, and no-see-ums all make their mark. Sometimes I forget, however, that humans are not the only recipients of their unwanted attention. For example, my good friend Dr. Art Borkent studies a group of flies called the Corethrellidae, whose mosquito-like females feed on frogs and are attracted to frog calls. But Art’s main study group are the aforementioned no-see-ums, technically known as Ceratopogonidae. The many species of these minute flies have differing ways of life, as some are predators of other insects, some are misery inducing biters of vertebrates (especially on beaches, where they can clear the humans out during certain times of day), and surprisingly, some feed on the “blood” (haemolymph) of other insects.

We saw a spectacular example of this yesterday here in Costa Rica. We took a day trip to a spot called Las Minas, where we were looking (mostly unsuccessfully) for different ant-decapitating flies. While searching around, Wendy Porras, our Costa Rican colleague, found a katydid with something strange on it. Being an excellent field biologist, Wendy immediately recognized that this white, almost pea-sized attachment to the katydid’s abdomen was a swollen female ceratopogonid, full of eggs.

ceratopogonid on katydid's back

I hope Art will forgive me, but I didn’t collect the specimen. I got distracted by other things, and by the time I thought of it, the fly had already left. This is a case of bad field work on my part. Certainly when significantly unusual things are seen, they should be collected so that the specimens accompany the life history observations. Hopefully we can make up for it with even more significant observations on the phorid flies that we came here to study.

closeup of the fly

[Thanks to A. Borkent for a couple of corrections to the original post]

Field work

For many of us, going to the field is what we like most about Dipterology (the study of flies). The chance to find new species, experience different environments and cultures, and more than anything, the opportunity to slow down; these are the rewards of the field.

I am on an airplane to Brazil to work with my colleagues Dalton Amorim and his PHD student, Danilo Ament. We have a long-term collaboration based on shared work on phorid phylogeny, thoracic morphology, and tropical inventory. Camaraderie is another pleasant aspect of field work.

This time, we are going to Rondonia, in the southern Amazon. It promises to be a trip of amazing discoveries, as very little collecting has taken place there, other than at Rancho Grande, a formerly popular collecting site that apparently doesn’t have any forest any more. We are going to stay at another area, called Monte Negro, and make excursions from there. Every day (I hope), I will post about our finds, to give the flavor of a tropical Diptera expedition.

For now, I’m just trying to endure the long flights…

A wasp-mimicing flower fly from my last field trip in Costa Rica

Gardening for flies, part 2

Having had my garden for about three months now, I can say that there is always something interesting to see and photograph in it. Regular visitors include many flower flies, commonest of which is the little blood red flower fly, Paragus haemorrhous, followed by Allograpta obliqua, Syritta pipiens, and a Platycheirus species. During the sunny parts of the day, there are ALWAYS flower flies.


Another group of frequent visitors are bees. Mostly, however, they are not the common honeybee; instead, they are native bees that are much more welcome, in my opinion. Native bees do not sting people unless severely provoked, and they come in a variety of shapes and sizes from tiny little, almost gnat-sized bees to lumbering fuzzy bumblebees. They are generally faster moving than honeybees, and thus more difficult to photograph, but if you focus on a popular flower and wait, you can usually catch them eventually.

      Finally, there are the occasional visitors, that show up to feed on specific type of pollen. Among them are a couple of types of beetles, including dermestid beetles (shown below) that are occasional household pests, and the wedge-shaped tumbling flower beetles of the family Mordellidae.

all photos are copyright B. Brown, 2011. all rights retained

Gardening for flies

 Brian Brown’s instant flower fly garden 

                It probably doesn’t occur to many people to collect plants specifically to attract flies to their garden, but during my work on flower flies, I started getting more and more interested in photography again. I could go to the Arboretum, or somewhere else with many flowers in order to photograph interesting flies, but I wanted something closer to home. Also, I started thinking about what would be an optimal garden or collection of plants to attract flower flies. I needed to do some research. 

A flower fly - Eupeodes fumipennis

Flower flies are generally considered a gardener’s friend. The larvae, or maggots, of the most common backyard species feed on aphids, scales, and other softbodied insects. By attacking the gardener’s worst enemies flower flies become a potent ally.

 In order to make these allies more welcome in our backyards, it is necessary only to plant a few, low-cost flowers. These provide the nectar and pollen that flower flies need to fuel their flight and mature their eggs, respectively. Not just any flower will do, however. Flower flies appreciate flat flowers whose pollen is easily reached. They also have different requirements than honeybees, so planting a garden for flower flies will not attract swarms of stinging invaders. It will attract native bees, though, which provide a welcome addition to the flower fly parade.

 I wanted to see which flowers would be best for attracting flower flies to my backyard, so I went to my local (Los Angeles area) nursery and just watched the activity in their displays. It quickly became apparent that flower flies were concentrating on just a few of the offered scores of plants available. Therefore I bought one plant or flat each of the flies favorites: Japanese Photinius, pink and purple cosmos, white “mini-margarite” daisies (Chrysanthemum paludosum), and yellow Argyranthemum. The total cost for my mini garden was $18. I brought them home, set them in the sun, and waited.

 Within half an hour I had flower flies coming to them. Instant success! Since then, I have had a continual parade of flower flies, native bees, and other interesting insects to enjoy and photograph. I also added a couple more plants: sweet alyssum, which is another flower fly attractive plant I observed in the nursery, and bog sage, something I’d seen attracting many flies at the Arboretum. I put the whole garden in four plastic pots for more maneuverability.

 This low-cost, minimal garden will bring a constant supply of colorful, beneficial insects to your yard, which will increase the number of predators attacking aphids and other pests, and boost your backyard biodiversity. It takes up so little space that it could even be put on a balcony or postage stamp lawn and still be successful. Of course, if you have more space, you can put out more than one of each plant, and you will probably attract even more interesting creatures.

Instant Flower Fly Garden

Next posting: what has been attracted to my instant garden, and which plants are best.