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Some Tips for Raising Caterpillars

Finding eggs and caterpillars is easy — especially if you plant host plants in your garden. If you plant parsley or fennel, it is almost guaranteed that you will have black swallowtail eggs laid on your plants. This is a good species for the beginner as the caterpillars and host plants are plentiful and easy to raise.

Use a toothpick, twig or a piece of paper toweling to move caterpillars — avoid touching them with your hands to limit transfer of disease-causing germs and to prevent possible injury to their delicate bodies and feet. Also keep in mind that some caterpillars can deliver an unpleasant sting.

When collecting or moving caterpillars, try using a scissors to cut the piece of host plant they are attached to. This will reduce the possibility of causing a life-threatening fall. To transport your finds, a small lidded plastic container will keep the critters inside and protect them from being crushed accidentally.

Dedicate a separate cage to each species of caterpillar you try to raise.

A little bit of research and observation will let you know what besides the host plants your caterpillars might need. Swallowtails, for example, like to attach their chrysalises to a rough stick. Putting a couple of pine twigs in your cage will make for happy caterpillars. This does not mean that some will not choose to attach to the side or top of your cage.....

Regular cleaning of the cage is essential to prevent caterpillar diseases. Once you have removed the caterpillars and host plants from your cage, if not using some sort of paper toweling, try picking up the frass with a Dustbuster-type portable vacuum. You might find a miniature dustpan and brush are also handy.

Keep your cages out of direct sunlight. Excessive heat will harm the caterpillars.  In addition to trying plastic-wrap covered glasses or florist tubes to hold host plants in water, try a plastic film container. Poke a hole in the plastic lid to insert the stems.

Your powers of observation will hold you in good stead. The more you watch caterpillar behaviors, the more you will be able to anticipate the needs of your charges. Check on them daily to be sure they have sufficient food and a clean cage.




Suggestions for Constructing a Caterpillar Cage

— from the Ridiculous to the Sublime

by Ruth Burch

Regardless of what it is about butterflies and moths that enthusiasts find most appealing, most of us have had or will have an opportunity to collect eggs and caterpillars to raise. Figuring out what container will serve best as a rearing cage may be the biggest challenge in this endeavor, so here are a few ideas to get your creative juices flowing.

When construction time, design complexity or cost are primary concerns, a ridiculously simple cage can be made from a cookie tin and window screening. The top and bottom of the cookie tin are used as top and bottom of the cage, and a cylinder made of screening placed between them is the only other structural part. Even a first-timer can finish putting one of these cages together in less than 30 minutes after gathering a few materials. 

Cookie tins, when not stashed in the attic or the dark regions under the kitchen counter, are generally available at yard sales, thrift shops and general merchandise stores for a dollar or less. For most cage needs, I prefer tins with at least a 10-inch diameter and a 4-inch or less depth. The metal most tins are made of is not rust-proof; if the cage is to be left outdoors, it will need to be on a porch or under cover of some sort to keep it dry.

Window screen can be purchased by the foot at most hardware stores. Aluminum screening is available in shiny silver or black, which many feel is easier to see through. Foot-lengths of 36-inch silver screen are about a dollar, with the black costing about a dime more per foot. Aluminum screening is preferable to the fiberglass type as it is stiffer (making the cage sturdier) and tougher (making it less susceptible to pecking birds when cages are left outdoors).

On most cages, a finished height of about 14 inches works out nicely. I add two inches at the top and bottom of the cylinder for a double-folded "hem" (method described below). By getting the 36-inch length screen and using ordinary scissors to cut it into two 18-inch lengths, slightly less than three feet of screen is needed to make cylinders for two 10-inch cookie tin cages (about a 31-inch circumference with a 2-inch overlap) — a screening cost of about $1.50 per cage.

Once the screening material has been selected, measured for both desired height-plus-hem-allowance and circumference-plus-overlap, and cut, lay the screen on a flat surface and fold over about one inch. Use a yardstick, scrap board or something similar to press down the first fold. Then fold it over again so the rough edge is sandwiched between two layers of screen. Press the edge of the second fold. Repeat the folding and pressing steps at the other end of the screen, making sure both folds will be on the same side of the screen. The folded hem not only adds sturdiness to the cylinder, but also puts rough edges safely out of the way.

The next step is to make the flat screen into a cylinder. An ordinary office stapler can be used to secure the screen, or you may want to try using florist’s wire or stiff, waxed string/thread to stitch it closed. As I am usually rushing to construct a cage, I prefer the quickly stapled closure. After curling the screen into a cylindrical shape with the folds on the outside and the straight, smooth, surface on the inside, fit the screen to the intended cage base. Allow enough screening for the cylinder to slip in and out without binding, but it is best not to make it too loose. Put staples near both edges of the overlap and use as many staples as necessary to eliminate gaping holes. Where your stapler cannot reach, use unbent staples and close them with a screwdriver edge. The rough edges of the overlap are not often a problem for the insects or the people tending them since they are secured closely to the wall of the cylinder. (Society member Don Denault likes to add a stick to staple the edges onto; he finds the stapling easier and the cylinder sturdier.)

All that is left to do for this cage is to put it together! I like to use a sheet of paper toweling to cover the bottom of a cage. This makes it easy to see frass (caterpillar poop) — a certain indication that the critters are eating the food being provided — and facilitates quick cage cleaning every day or two to keep them healthy. After laying a paper towel over the top of the base, use the bottom edge of the cylinder to push it neatly to the floor. Add fresh host plant in a glass of water covered with plastic wrap to prevent the caterpillars from falling in and drowning or place the food in florist tubes arranged in an empty glass. Now you are ready to settle the caterpillars into their new home.

A more sophisticated looking cage, requiring more carpenter-like planning and skills, can be made from an aquarium. Advantages of this type of cage include better visibility and that the weight and rigid walls of a glass or plastic structure make it very stable.

The smaller aquariums, ten gallon capacity or less, are easy to find at yard sales and thrift shops — and it will not matter for this purpose if they leak. Designing a lid is relatively easy and can be kept simple. Because many of the caterpillar species like to make their chrysalises suspended from or attached to the underside of a horizontal surface, a rigid lid is preferable to one made from, say, a soft fabric with an elastic edge. My live-in carpenter (my husband, Glenn) designed a picture-frame-like lid from wood strips and molding. Aluminum screening is secured between the wood strips which cover the top of the aquarium and the molding which is fitted to the inside dimensions of the aquarium’s opening.

With the lid removed, it is very easy to arrange or change a layer of paper toweling for the floor of the cage. This large opening is also handy for placing the host plant container.

On the sublime end of the caterpillar cage design spectrum is the type of cage crafted by late Society member Don Denault. Reproduced here are the design specifications for a small Denault structure made of salt-treated wood and window screen. While the cost and time requirements are greatest for this cage when compared to the other cages discussed, the advantages should be considered. These deluxe accommodations for your caterpillars will most likely last a long, long time and are certainly the best-suited for leaving outdoors without being overly concerned about an occasional rain wetting. The outdoor cage is also most convenient for releasing the newly emerged moths and butterflies with the least amount of hauling the cages out and back. (Our household enjoys keeping our cages indoors where we can most closely monitor changes, behaviors, and activities of the caterpillars, but many folks are put off about having bugs in the house on purpose.)

The cage designs suggested here barely scratch the surface of the ideas listed in various field guides and other references. The possibilities really are endless, and you will want to incorporate your own ideas as you gain experience with this fascinating aspect of butterflying. But whether your design choice is from the sublime or ridiculous end of the spectrum — or somewhere in between — go ahead and give raising caterpillars a try.

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