This post contains photographs and construction tips for a killer craft I made: an autocidal gravid ovitrap. Pregnant females enter the trap, lay some eggs on or near the stagnant water within, then are prevented from exiting and die. Their progeny also die because a screen at water level prevents larvae from reaching the surface to obtain oxygen. When similar traps have been deployed they bring down mosquito levels substantially and thus are quickly becoming one of the main ways to prevent mosquito outbreaks and disease. Every homeowner should have six. They’d make wonderful gifts.
The design features a clear dome that helps trap the females when they are done ovipositing (they go for the light), plus a completely unneeded observation window so I can watch the larvae and pupae (fun for the whole family, plus good for demonstration purposes). It borrows general methodology from gravid Aedes traps (GATs) designed by Dr Scott Richie (James Cook University) and colleagues that recently made news on NPR (here’s an overview; here’s their paywalled journal article). I’ve designed mine to capture species that also lay egg rafts, so it’s not just a GAT. My design doesn’t use insecticide because I wanted the odor of developing larvae to be an attractant to other females (it is, by the way).
What you need
6″ plastic pot
clear dome from cake store
metal coat hanger
small neodymium magnet
silicone adhesive glue
1-L soda bottle
1/4″ foam weatherstripping
black spray paint
Dremel tool with cutting bit
drill with drill bit
safety glasses (when Dremeling)
If you’d like to see photographs larger just click on first image and navigate like a slide show. There are many ways to construct these so if you build one and it looks completely different, don’t worry. This is because if your device is the only stagnant water around, females will use it.
Buy an 8″ cake for the clear dome on top. Eat cake.
Cut off bottom of pot, use knife to smooth edge.
Draw circle on dome where funnel will drop in.
Cut hole in dome with Dremel to accommodate funnel.
Glue funnel onto dome. Use Goo Gone to remove labels.
Fit funnel with optional hardware cloth grid.
Cut hole in pail lid with Dremel, then smooth the cut with a knife.
Cut observation window into side of pail.
Cut rectangle out of soda bottle for viewing window.
Glue soda bottle plastic onto inside of observation hole.
Apply bead of silicone sealant to outside of observation window.
Cover observation window prior to painting.
Paint outside of pail and lid black.
Attach clear dome to pail lid with anything but Goop
Bend coat hanger into diameter equal to inside diameter of pail.
Staple fabric screening onto coathanger.
Affix weatherstripping to inside of pail to support the screen.
Make handles for the screen out of paperclips.
Drill drain holes so that water line is barely above screen.
Fill pail with rainwater not tap water.
Add old leaves from gutter, cat food, etc. to bait the water.
Add wood (and/or cloth strips) for egg laying.
Hang sticky card by paperclip held by neodymium magnet.
Situate trap in thick vegetation, protect from rain somehow.
I’ve only just deployed it and it’s rather cold right now so I don’t have any victims yet. But I’m optimistic and am posting now with the hope that somebody will have suggestions on how to improve the design (I’m making more). One improvement I’m definitely going to make is to drop the funnel lower into the dome so it’s harder for females to accidentally fly straight up to escape. And pro-tip if you make the above: attach the lid to pail when spray painting to avoid unwanted buildup where they attach.
I’m also posting in the off chance that a biology teacher might take an interest. Having teams make these would be really fun and then they could deploy them in the woods near the school: bonus points for team that traps the most mosquitoes. It’s fun like the classic egg-drop lab in physics except useful. Students would then take their projects home where they’d continue to be useful. Would make for a great Girl Scout Gold Award / Eagle Scout project.
Last week when I was at Ridley Creek State Park I crossed paths with a tree tour led by wildlife biologist Gary Stolz (PA Dept of Conservation and Natural Resources). I promised the group that I’d post photographs of things I’d seen at the park. Here are the highlights:
Long-tailed giant ichneumon wasp
The largest and most colorful was clearly the long-tailed giant ichneumon wasp (Megarhyssa macrurus) that I found ovipositing into a red maple. Actually, there were perhaps a half-dozen of them, all presumably targeting the larvae of Tremex columba (a sawfly) that were busy eating the tree. The presence of the sawflies is given away from probably a mile away (I’m guessing here) due to the odor of the symbiotic fungus they use to help digest the wood. Once on the tree, though, the ichneumon probably locates a larva by sensing the vibrations it makes when chewing. The ovipositor is approximately 2″ long and is tipped with a cutting edge (as you might guess). It also drips out a fluid that helps dissolve the wood. An amazing insect to watch.
Green’s giant ichneumon wasp
Also on the same tree were several Green’s giant ichneumon wasps (Megarhyssa greenei). This species has a shorter ovipositor (among several other differences) but does pretty much the same thing as the species above.
Unknown wasp in Tribe Ephialtini
Also beautiful but much smaller (perhaps 12 mm), I found this wasp ovipositing into a nearby tree that was completely dead and covered with moss. I’m still working on an ID (it’s something in the Ephialtini). Which means, like many of the insects I photograph, I’m hoping that an expert will eventually help me identify it. Sometimes that process can years but I’ll update this page if there’s any movement. For those curious, I post photographs to iNaturalist and BugGuide for help. And I often ask my Dad (Foster Forbes Purrington), an entomologist.
The last wasp of the day is Coelichneumon navus, another ichneumonid but with a concealed ovipositor. This species has been known to parasitize fall webworm (Hyphantria cunea) and cypress looper moth (Iridopsis pergracilis), but like many of the 100,000 or so members of the family Ichneumonidae not much is known about its natural history. I found two caterpillars on this tree but haven’t yet ID’d them.
Another insect with no common name, Gnophomyia tristissima live, love, and die around rotting hardwood logs. These are crane flies and can be identified by their bright yellow halteres (remnants of their second pair of wings) and black bodies. This photograph shows mating but afterwards the male seems to guard the female while she oviposits (if you want to see that, click on image to be taken to a site that has additional photographs). I spent about 30 minutes watching and photographing them and could have stayed longer. But the mosquitoes were exsanguinating me.
American nursery web spider
Earlier on my walk I found a rather orange American nursery web spider (Pisaurina mira). It was also rather large.
Banded fishing spider?
I can usually narrow down spiders given their eye arrangement and details of web (or lack thereof), but this is stumping me. My tentative guess is that it’s a freshly-molted (teneral), juvenile banded fishing spider (Dolomedes vittatus). I’m trying to get this confirmed so check back if you’re curious. Astute readers will notice that it’s on a tree, not near water, but apparently there are few members of Dolomedes that can live away from water just fine. This is one of those species.
Northern water snake
This was the first time I’ve seen a northern water snake (Nerodia sipedon) but apparently they are super common. This one was perhaps 2 feet long but they get as big as 4 1/2 feet. Non-venomous, though, in case you were wondering.
I’m still working on an identification but my current guess is sulphur tufts (Hypholoma fasciculare). Or, if you prefer, sulfur tufts. I really enjoy photographing young mushrooms but the consequence is that they are harder to identify.
That’s it! If you have any questions, send me a note or leave a comment.
iNaturalist is a free site that allows nature fans to share — and learn more about — organisms they’ve found on hikes, in their yards, or attached to their bodies. All you do after signing up is upload a photograph, make an identification guess (or not — no pressure), then solicit ID help from the built-in AI as well as from the approximately 80,000 active users, some of whom know how to identify things. But it’s a community, so you (yes, you) can also weigh in on IDs for photographs taken by other members (but again, no pressure).
Below are some reasons to give it a try. The first several are general, the later ones for scientists or professional naturalists.
1. Get your photographs identified
If you post nature pics on the Internet, it’s so much better to caption them with either common name or Latin name so that people can easily find the image in Google searches and such. Plus people just like to know. Saying something is a “seal” is fine but when you have a Galápagos sea lion you should say so (because there 12+ species of seal). You should also use iNaturalist even if you think you know what it is. E.g., to make sure you’ve captured a Galápagos sea lion not a Galápagos fur seal, both of which are in the Galápagos. Using iNaturalist to get IDs is also better than posting a photograph to Twitter, Instagram, or Facebook and asking the world, “Anyone know what this is?” Your followers on those other social media accounts might not be giving you accurate information. Just saying.
2. Educate yourself
Nature in the general sense is nice and all, but after you figure out exactly what something is you’ll have the magic key to find further information that might be truly interesting. E.g., Nazca boobies (Sula granti) have an interesting name but if you Google the name you can learn that males court females by offering them sticks and stones even though this species doesn’t even build nests (behavior is an evolutionary holdover from ancestors that did, presumably). Another reason to search for more information is to be reminded that for the vast majority of species, even rather common ones, we know surprisingly little. And knowing this is a good thing because then youngsters and young at heart will realize that going into a biology-related field is a way to explore the unknown. Appreciating and protecting life on earth is easier when you know the details, and you can’t get them just by knowing a lot about polar bears and other charismatic megafauna.
3. Use and improve your ID skills
Your friends and family might roll their eyes whenever you call out bird names when one zips by, but those identification skills are cherished on iNaturalist. Nobody will make fun of you! By providing IDs you are helping those new to nature get more out of nature and in, perhaps, helping voters and politicians appreciate see that policies can directly help or hurt particular species on the planet, even in your home town. You will also be providing IDs to over-educated professionals who might be posting pics of organisms outside their research speciality, but who might someday return the favor. iNaturalist also provides an environment where you can teach yourself how to ID new organisms. E.g, I learned that great frigatebirds (Fregata minor) can be distinguished from magnificent frigatebirds (Fregata magnificens) by their green sheen. Tricks like this can be useful when traveling to new places, and you can use iNaturalist like a study guide to prepare for such trips. E.g., if you’re shelling out tens of thousands of dollars to travel to exotic places like the Galapagos, spend the year before learning the flora and fauna so that once you land you know what’s going on (your guide might not). All you do is subscribe to the place and challenge yourself to learn how to identify submissions (you’re going to need a few books, too).
4. It will make you happier and healthier
iNaturalist is like a mental Fitbit, recording what you’ve seen instead of the number of steps. And then when you revisit memories of being outside you’ll become happier! At least that’s the research. I’m just hand-waving here that iNaturalist will make those memories fonder and more vivid, but it’s not too much of a stretch. At the very least it’s true for me. It’s also reasonable to think that if iNaturalist motivates you to go outside more often, losing excess weight or achieving those 10,000 steps will be that much easier. But I’m not a real doctor, so consult your physician to see whether nature is right for you. And please check for ticks (take a photo if you find them).
5. Meet interesting people
People who are active on iNaturalist are by definition curious and have open minds. Those are the peeps you are looking for these days. Right? Unlike some other social media places, users are also actual people … and some of them live near you. So when you see on iNaturalist that there will be a meet-up at a local park, join them. Or if you’re in one of those areas where iNaturalists are rare and shy, you can organize an even and invite folks.
6. Be a better parent
If you have young kids who are still fascinated by nature instead of electronics and air conditioning, encourage this interest by modeling a similar interest, even if feigned. If, for example, your little girl is fond of spiders, take pics of the ones she finds, upload to iNaturalist, then show her the eventual identification results and help her Google the species name for more information. You don’t need to have a biology degree to do that.
7. Be a better teacher
If you’re a biology teacher, you really, really need to become proficient in iNaturalist. E.g., if you teach kindergarten and want to tap into kids’ innate interest in nature, submit pics of organisms that your students find in the classroom or during recess. You can say each Monday, “Good morning boys and gorls — find me an organism!” You take a pic, then share ID, courtesy the folks on iNaturalist, with your students on a subsequent day (oh, the suspense!). Pair those IDs with an age-appropriate book on very hungry caterpillars, itsy bitsy spiders, or whatever. And if you’re a college teacher, you could assign a local, interesting species to each of your students, tasking them with (e.g.) figuring out how to ID it and to explain its distribution and conservation status … and after several weeks ask students to make presentations supplemented with natural history tidbits from the primary literature. Ideally, an exercise should challenge the students to contribute to iNaturalist (e.g., if they can make themselves an expert for species X, they should be able to weigh in on IDs). There are thousands of ways to incorporate iNaturalist into classrooms and homeschooling. iNaturalist has a page to get you started. Here’s a video tutorial if you like to watch.
8. Manage your land better
If you manage a natural area, you can use iNaturalist to create a permanent, dynamic, searchable database of all the species found there. It’s probably your job to do that in some regard, but iNaturalist allows you to crowdsource the task — just ask to visitors to upload their pics to iNaturalist and, voila. It’s really easy to set it up: draw a polygon around your area in Google’s MyMaps, export KML map file to desktop, upload map to iNaturalist to create a “new place”, then create a Project that automatically shows all observations in your area. The setup process takes approximately 15 minutes. If this sounds useful, just do it right now but tell your boss that it took weeks.
9. Get alerts when a species is observed
If you are in charge of tracking the spread of spotted lanternfly, emerald ash borer, or any of the other thousands of invasive species that keep biologists up at night, just “subscribe” to that particular taxon for the park, county, state, or country of interest, then sit back and wait for the email indicating that somebody has found that species area of interest. It’s so much better than all those report-an-invasive apps or 1-800 numbers that require people to know that something is invasive and also be motivated to download an app or look for number to call. You can also use the subscription feature to monitor a place for a species that might be your research focus (e.g., perhaps you want to know when the Galapagos carpenter bee colonizes a new island).
10. Mine it for data
There over 12,700,000 observations on iNaturalist, and that means if you’re looking for something rare or just trying to quantify something, you might be able to extract data to address a hypothesis from the comfort of your couch. For example, you might want to know whether marine iguanas close their eyes when they sneeze but don’t want to make the trip to the Galapagos to find the answer (though you probably do). You can also track when a species is first seen flowering in an area for the past 10 years … which might have something to do with climate change. Or you might notice that there’s a new, undescribed species (!), in which case you can contact the observer, write a paper together, and be famous (some examples). Finally, if you need DNA or measurements from a particular species you can hit users up to do this. My suggestion to scientists and teachers who are too busy is to just sign up and then subscribe to your study organism, something that will take 5 mins, max. Once you start seeing variation, natural history comments, and interesting questions from users you’ll be hooked. The are numerous ways to make it interesting and useful … you just have to toggle the settings in the right way.
I have more reasons why you should be using iNaturalist but 10 is the limit for lists of 10 so I’ll end here. Thanks in advance for sharing this post with your friends. We need them, too.