Bug Blog

Cactus Killers – Cactus Longhorn Beetles

Cactus Killers – Cactus Longhorn Beetles

The noble cactus is a plant particular to the southwestern United States, particularly the Sonoran Desert. While the desert may seem like a barren wasteland, it is actually teeming with life and, of course, this includes insects. Just like any other plant, shrub, or tree the cactus has its own pests that like to hang around and generally cause harm and bring disease to these tough plants. One of the most fascinating and well-known insects that flock towards cactus is the cactus longhorn beetle. They are rather terrifying with their long antennae and frightening mandibles, but are truly distressing to people trying to grow healthy cactus in their garden or yard.

The cactus longhorn beetle comes in at an inch long or more, with a shiny black body, fused wings, and large antennae. They have a rather hunched stance and their elongated head almost looks like a horse’s. If you happen upon one if these, they do look like they could do some damage. However, it is not the adult cactus longhorn beetle that poses a threat to cactus, but rather their larvae. Their larvae have ferocious appetites, and if left to their own devices will feed so much on the cactus that they can cause serious damage to even large cacti. Wherever they feed, that spot will then soften due to the lack of support, which the larvae have consumed. These soft spots can eventually collapse in on itself the more tissue the larvae eat. Thankfully, this isn’t a concern too often, as the larvae of the cactus longhorn beetle have many natural predators to take care of them. There are, however, situations where gardeners do need to be vigilant in protecting their cacti from the larvae of the cactus longhorn beetle.

The female cactus longhorn beetles will lay their individual eggs in different spots of the cactus where the eggs will then hatch into brown headed larvae that burrow inside the cactus to get their food. The larvae secrete a green substance into the whole as they burrow inside, which hardens and turns black. This keeps their entry point secure, allowing them to feed on the tissue inside the cactus and the roots. They will spend the winter inside the cactus, eating away at it, and finally emerge as an adult in the spring. If you spot a cactus longhorn beetle on your plant, then it is highly likely there are also larvae on it as well. Whole you might not be able to get at any larvae inside, you can prevent the adults from being able to hatch future eggs that will eat your plant alive. You can easily pick off the adults, and you want to catch them before they’ve had a chance to hatch another generation of beetles.

Have you ever seen a cactus longhorn beetle? Where did you see it and was it on a cactus?