What’s Wrong with My Cactus?

No, that’s not cotton candy clinging to the pads of your prickly pear plant. It’s actually a harmless scale insect that not only feeds on the plant’s moisture and nutrients, but is also used to produce a brilliant (Christmas) red dye.

It’s a common sight in San Antonio, that white cottony substance on the pads of Opuntia (prickly pear) cacti. Have no fear — this strange material is not a disease, but actually the native cochineal insect. While it is a parasitic insect, it does not significantly harm the cacti.

The cochineal insect is of the genus Dactylopius, with many species occurring in the western hemisphere. Identification of the exact species is difficult, even for seasoned entomologists.

Historically, the insect was used to produce a brilliant red dye, derived from the carminic acid found within the female insect’s body. At the time of the Spanish conquest, red was a highly sought after color in Eurasia and was only available from the madder plant. Cochineal became a major export from the New World in the 1500s until the invention of synthetic dyes in the mid-1800s. Cochineal was number three on the list of important exports from the New World after gold and silver. Before the Spanish conquest it is said that the Aztec ruler, Montezuma, received yearly tribute from conquered cities in bulk cochineal.

While this form of dye production has been replaced with modern methods, it continues as a historically and culturally significant process that has regained popularity since concerns have been raised over the health effects of synthetic dyes.

As a knitter who appreciates natural fibers such as wool, cotton, silk, etc., it only makes sense to obtain colors from natural materials such as cochineal. Other historically used dye sources include black walnut, turmeric, some fungi, indigo and goldenrod to name a few. Different shades and intensities of color can be produced depending on the process used. One can marvel at the subtle variations in color sourced from these natural materials as they seem to be easier on the eyes than some of the more commonly available synthetic dyes.

So don’t worry! This little bug is not going to hurt your plants. In fact, it’s a living reminder of times past when people spun their own fiber into yarn, wove that yarn into fabric and dyed it using natural means.

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Sarah Galvan
Sarah Galvan has been passionate about gardening since she was a child. She’s an arborist, herbalist, Texas master naturalist, a former SAWS conservation consultant and holds native landscape certification. Galvan worked as a native landscape designer where she focused on supporting native bird and pollinator populations. When she’s not answering gardening questions or working on her biology degree, Galvan enjoys hiking, kayaking, bird and butterfly watching, and competing in plant identification competitions.
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