I’ve been on several insect collecting trips with my students recently thanks to my position as teaching assistant and official bug collecting expedition guide for insect systematics. I like to collect, so it’s been a great way to spend a semester so far! Last week, I took a few students to a local park after work to collect until dusk and blacklight after dusk. (If you don’t know what blacklighting is, I’ll be posting about it soon!) Ultimately, we got there a little too late in the day to get much while it was still light, but I did come across this:
Prickly pear cactus.
Even though this is a very common sight in the southern US, Mexico, and parts of South America, a lot of people son’t know what that white gunk on the prickly pear cacti is. I can’t really blame them. After all, this does look a whole lot like a fungus or some bizarre, super fast growing lichen:
Fluff on prickly pear.
And if you pull some of the fluff off, it gets even more bizarre when you find these little round blobs under the fluff:
Little round, reddish blob in fluff.
Some people think these are ticks full of blood and others think they are a type of plant mite. Others can’t see any legs at all and have no clue what they are (rocks? seeds?). Most people only know that is that when you see these on your cacti, you end up getting dense mats of white fluff full of little round blobs all over the plants. So what are they?
Meet the cochineal bug:
That’s right! That little round, indistinct blob is an insect! You might have a hard time identifying the 3 body segments, the six legs, the mouthparts – even trained entomologists can’t always distinguish them! – but these are insects. They’re just highly modified insects that fill very specialized roles.
Cochineal bugs belong to the insect order Hemiptera which makes them one of the true bugs. (See my post on true bugs for more information about the order.) Within the Hemiptera, the bugs are divided into three suborders: Heteroptera, Auchenorrhyncha, and Sternorrhyncha. Most people are familiar with the heteropterans, which include a lot of our common bugs such as plant bugs, stink bugs, assassin bugs, and the group I study, the giant water bugs. Most people also know something about the auchenorrhynchans if they’re familiar with cicadas, leafhoppers, planthoppers, or treehoppers. Apart from the aphids and whiteflies (both serious pests of crops and gardens), the sternorrhyncans aren’t nearly as well known by the general public. It’s too bad. The group contains some of the most gorgeous and alien looking insects, including the scale insects, the group to which the cochineal bugs belong.
Scale insects are bizarre, even by entomological standards. Most of them are herbivores and several species specialize on one specific type of plant. The cochineal bug, for example, loves prickly pear cacti (Opuntia spp.). Most scale insects exhibit funky structural modifications including reduced or absent legs in females, loss of the wings in females, strong reduction of the hindwings in males, and larviform bodies in adult females (i.e. they look like caterpillars as adults rather than looking like normal insect adults). The females of many species, including the cochineal bugs, are sessile. This means that they hardly move at all, preferring instead to remain in one place. They simply plug their piercing-sucking mouthparts into the plant and spend most of the rest of their lives eating plant juices in the same spot until they get so fat they can barely move. (If you’ve seen the movie WALL-E, imagine the people on the spaceship and you’ll have a pretty good idea of how female scale insects spend their lives!) The males usually have wings and fly around looking for females to mate with during their 1-3 day adult lifespans. The nymphs that hatch from the eggs they produce are call crawlers. Crawlers, as the name suggest, have legs of a more normal size and are much more mobile than the adult females. They can move around the plant to explore until they complete their hemimetabolous metamorphosis and become adults. If they’re females, they’ll spend most of the rest of their lives on one tiny patch of plant, often secreting waxes that can take on some very complex forms. In fact, because the adult females are basically little sacs of fluids and barely have any features to use for identification, the shape of these waxy secretions are essential for identifying several scale insect species.
Cochineal bugs secrete waxes too, which is why you find them under those white, fluffy patches on the prickly pears. Like many scale insects, cochineal bugs tend to be colonial, so you will often find large numbers of them living on the same plant. So, if you see prickly pears with paddles that look like this:
Prickly pear paddles covered in cochineal.
they are hosting a large colony of strange little insects hidden under the piles of fluff.
Cochineal bugs may not be terribly interesting behaviorally since they mostly sit in one place eating, but they are extremely important culturally. Take a look at what happens if you accidentally squish a cochineal bug while trying to collecting it:
Red spot on my finger.
Remember, these are nearly immobile little blobs of plant juice so they’re not biting me. And no, I didn’t have a close encounter with the cactus I was collecting from! That red spot isn’t my blood. It is cochineal hemolymph (the insect equivalent of blood) and it is red because it is full of carminic acid. Carminic acid can be extracted from the bugs and mixed with salts to form carmine, a highly valuable, bright red dye. So where might you find this dye in use? Well, many people are familiar with the exquisite hand-woven rugs of the Navajo. The bright reds, pinks, and some oranges you see in their rugs are brought to you by cochineal bugs! British redcoats? Cochineal bugs were imported from the Americas to dye the fabrics used in army uniforms. The pink color in your delicious strawberry milk? Check the label. If you see dye E120 or carmine on the label, you’re drinking extract of cochineal bug! That’s right, we still use cochineal based red dyes for fabrics, foods, cosmetics, some paints, and other products. There are even massive farms devoted to producing cochineal in South America specifically so they can be used to make carmine dye. Harvesting cochineal is hard to do, but it also fetches a high price. According to Dr. Marcel Dicke’s TED talk, a gram of dry cochineal is worth more than a gram of gold!
So there you have it. That fluff on the cactus at the park was hiding a mini-gold mine of little, immobile insects. Someday I’m going to get around to collecting a bunch of these, drying them, grinding them up, and making the dye myself. I haven’t decided what to dye yet, but I think it will be a fun project. I’ll post the results here! If you want to give it a try yourself, you can buy dry cochineal online. This packet:
is available in England and fetches £3.10. The website also includes information on how to dye wool, silk, and cotton with dry cochineal. There are sources of cochineal within the US as well. Just search for dry cochineal sales online and you should be able to find several sources.
Next time, I’m doing a quick post on a fun caterpillar my students found yesterday, and then I’ll start my summary of my dragonfly swarm data! If you’ve been interested in that project, it’s time to tell you what I’ve learned from the information my readers have sent in. I’ve been absolutely astounded by the success of this project, so I’m looking forward to sharing my results!
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