North

Collecting Systems for the North

The example below is what I prefer for monitoring of catches of 100 - 500 flies. This system is stable and easy to maintain. It can accommodate catches of even 1-2,000+ flies if the sleeve is long and well spread out. It keeps flies in pristine condition for identification, and it almost never fails, even in very windy environments. Adapt the principles below to cheap, locally-available materials to suit the size of the catch, and collection objectives.

Collector Setup 20k

Materials

	Two clear 2-litre plastic bottles, one rigid, one more flexible
	Flexible Pole, e.g. five feet of 1/2 inch CPVC plumbing pipe
	Thin flexible wire, e.g. 20 gauge galvanized wire
	Polyester braided sewing elastic, e.g. 1.8+ mm diametre 60% polyester, 40% rubber
	Transparent netting of suitable strength and mesh size
	White coat hanger

Start by attaching the flexible pole to the back support of the trap, extending it well forward. This will provide a point of attachment for tension to lift up and spread the cone. Any flexible pole will do (e.g. sapling trees). A retail option is 1/2 inch CPVC plumbing pipe (10 foot lengths, cut in half). It fits nicely into the groove of an iron T-bar, which is what I use for a sturdy back support pole. Drill a few holes in the CPVC pipe near the middle to provide points of attachment for the wires.

Bad Set DO NOT substitute PEX for CPVC (chlorinated polyvinyl chloride) pipe. PEX pipe is also sold for plumbing, but it is too flexible. CPVC pipe is semi- rigid and maintains tension very well over a long period of time.. It will, however, eventually become brittle, and will need to be replaced after about a year.

This is an example of a "poorly set trap" with a sagging and creased cone. This trap was set with the wrong type of pipe (PEX); the outer poles were also not sturdy and sagged in towards the trap with tension produced by high winds. Despite these potential problems, the trap still caught about 1,000 tabanids.

A Practical Collector

Collector Closeup 26k

Soda bottle-top FUNNEL leading to open-ended plastic bottle CHAMBER
with Netting Sleeve and Netting closure attached with sewing elastic

	Cut the top off of a clear, smooth plastic bottle to make a FUNNEL for the apex of the trap cone (e.g. with an inner neck diametre of about an inch or 21 - 25 mm). Most 1.5 to 2 litre soda/water bottles made of thin plastic are about the right size and shape.
	*Use a wider funnel (e.g. 35 mm) in areas with large flies, or with many Hybomitra* horse flies** (e.g. a large juice bottle top). Hybomitra tend to accumulate at the top of the cone; a large exit hole helps to limit congestion, but may not eliminate this problem when numbers are particularly high.
	Cut the funnel shorter rather than longer (e.g. 8 cm high). If it is too long and the angle does not quite match the curve of the cone, there will be gaps between the funnel's rim and the netting. Flies crawl about in these gaps and have trouble finding their way into the collecting chamber (especially deer flies).
	Puncture double holes on opposite sides at the base of the neck of the funnel so that you can loop some thin wires through these points later. Make sure the bottom edge of the funnel is perfectly smooth so that netting does not snag and tear on any sharp edges.
	Cut off and discard the bottom half of the bottle. You will be left with a small section, the middle, smooth part of the bottle. This part is ideal for a light-weight SPREADER for the top of the netting sleeve.
	Cut off the top and bottom of a second, more rigid plastic bottle to make a cylindrical plastic CHAMBER into which you will later insert the neck of the funnel. Choose a bottle made of strong plastic (e.g. most 2-L juice bottles); ones with ribs are useful for keeping elastic bands in place.
	Cut a hole slightly smaller than the neck of the funnel in the centre of the chamber. Make sure this hole is smooth so that flies cannot escape through any small gaps. The slightly smaller hole in the chamber will buckle up when the funnel is inserted, making for a secure, tight seal.

	Snip a tiny hole in the top of the netting cone and insert the funnel from inside the trap, leaving the holes facing to the sides so that the chamber can be inserted pointing forwards.
	Insert a thin wire through the apex of the cone, looping it through two holes in one side and back out again through the netting. Try not to bunch up the netting and avoid tears. By looping the wire through two holes on each side, the wire does not need to run through the neck, which could interfere with fly movement. Temporarily attach the ends of the wire to the flexible pole, just to provide enough tension to make it easier to work on the other side. Loop a second wire through the other side as before.
	Spread out the wires and push the chamber down onto the neck snugly. If the receiving hole is the right size, the chamber will simply attach to the neck with enough tension to stay in place. The threads in the neck will also help to prevent the chamber from separating from the funnel. If in doubt, loop the wires around the chamber before running them up to the pole in the next step.
	Run both sets of wires up to the pole and attach with enough tension to spread the trap cone well. The entire top of the trap is supported by these thin wires with the tension spread out over the funnel. If you are careful in setting this up, the netting at the top of the cone should never tear and the entire system will be stable in even the strongest of winds.
	Close off the back end of the chamber by stretching a small piece of netting over the end; hold it tightly in place with a piece of sewing elastic. Rubber bands are not appropriate as they disintegrate after only a week or two in the sun. Thick sewing elastic will keep its tension for an entire season.
	Make a long (e.g. 50+ cm), loosely-fitting sleeve for the chamber opening from suitable transparent netting (the piece of netting cut out of the trap cone during sewing is about the right size). A fairly long sleeve is easier to change when there are wasps and hornets inside (common when flowers are abundant in early summer). Insert the light-weight spreader into the top of the sleeve. Slide the sleeve onto the chamber and hold it in place with a piece of sewing elastic.
	Angle the chamber slightly upwards so that flies will concentrate at the top of the sleeve, far away from the funnel. Stretch the sleeve to get a smooth fit and to keep it from bunching up in the wind. Use a coat hanger to suspend the top of the sleeve from the end of the flexible pole. Sew a netting tab into the top of the sleeve to hold the hook of the coat hanger. This way you do not have to run the coat hanger directly through the sleeve itself, which eventually produces tears in the bag. This arrangement is extremely robust, remaining intact even during severe thunderstorms. It is intended for routine collection of flies, so maintenance is required to remove dead flies which will accumulate in the chamber.

	A proper setup should look like this when viewed from inside the trap, looking up into the sky (here on a cloudy day). The goal is to suspend the trap with enough tension to produce a smooth cone without creases and folds. A second goal is to keep the exit at the apex as transparent as possible.
	When the catch is of no interest, reverse the orientation so that dead flies drop into a netting or plastic bag at the back. Punch holes in the bottom so that water can drain. A rigid container (e.g. aluminum screening) may be necessary if accumulations of dead flies attract birds or other animals.
	PVC /plastics may also be used for trap cones but will become dirty with time. This is an example of a well-used PVC cone that is still very transparent. Note the internal reflection of the sun off the inside of the PVC on the right. I am still experimenting with various substitutions like this, which can have major effects on the catch.
	Netting/screens will sometimes produce interference patterns depending on the mesh size, background and sun angle. The image at left is a metal screen inside a Cape Cod greeenhead box trap. The screen angles up at 45 degrees leaving a small gap for the tabanids to pass through into the cone.
Close-up of the exit in a trap with a PVC cone.
Practical Notes A funnel + chamber + sleeve collecting system can be troublesome to change when catches are high, especially if flies are active. To change the sleeve, bend the flexible pole so that the sleeve is sloping down, and shake the chamber sideways, but not too vigorously. You do not want to dislodge the sewing elastic holding the netting cover at the back of the chamber. You may also need to simultaneously blow from the back to get the last few flies down into the bottom of the sleeve if the flies are very active. Several seconds of shaking will usually get all of the flies into the sleeve so it can be quickly tied off, without the need to also blow. Watch out for yellow jackets and small wasps whenever changing very large catches; it is easy to miss them and get stung while holding onto the sleeve. Except for catches above about 500-1,000 flies per day, daily changes of the collector are OK. Early morning collections are best as flies are not active at this time, and mosquitoes will be in good condition. Evening collections should be done as late as practical. Fusca tsetse and many African stable flies are active at and after sunset. In Canada, some deer flies (Chrysops) are also still active very late or very early in the day.
Most flies enter the collector within minutes of being captured. They typically fly about inside the trap and repeatedly fly up into the apex of the cone, most often crawling out through the neck of the funnel. At very high densities, some species will accumulate in the trap cone, especially if the cone is not well-stretched, e.g. with creased edges or folds. If too many flies are accumulating in the cone and not entering the collector, then the size of the exit hole should be increased. This is a problem in northern areas with many large Hybomitra species of horse flies. They are much less prone to move upward than Tabanus and tend to rest inside the body of the trap. I have yet to test a practical solution for this phenomenon. Use of a hand-held vacuum collector (e.g. the "Dirt Devil") may be necessary for total counts of mosquitoes. Mosquito counts are also best done in the morning as some mosquitoes rest inside the trap cone, only gradually, or never, moving to the top of the cone and entering the collector. Mosquitoes remaining in the cone presumably die and fall to the ground where they are carried away by ants. I confirmed this was happening in 2008 by adding inner horizontal baffles to the trap to "catch" any flies that never find their way into the collector. This phenomenon was only common with mosquitoes.
It may be necessary to also vacuum black flies as they often simply crawl around inside the trap cone, rather than finding their way up into the collector. This is the behaviour I have seen with black flies at my home in Russell, Ontario, but this does not occur everywhere. In 2009, I caught up to ~30,000 black flies per trap per day in the Northwest Territories with most of the black flies routinely moving up into the collector.