Sticky Plants That Catch Insect Pests

By Larry Hodgson

Nearly 30 years ago, I grew some seeds of bat-face cuphea or Mickey Mouse plant (Cuphea llavea) I had ordered from Chiltern Seeds.

It gets its Mickey Mouse name from the tubular flowers with two rounded petals (mouse ears) in brilliant red. They are overprinted with a patch of deep purple, indeed, nearly black, that are supposed to look like the face of a bat (the origin of bat face).

Grown as an annual in temperate climates, bat-face cuphea is actually a subshrub from Mexico.

I started the seeds under fluorescent lights, as I do with most seeds, and they sprouted rapidly and grew quickly. But then I noticed something odd: there were the tiny black flies glued to its stems. You see, I was struggling at the time with a fungus gnat invasion. To my great surprise, the little pests ended up sticking to the stems, leaves and even the flowers of the cupheas, all of which have a distinctly tacky texture. The gnats seemed unable to free themselves and soon died. I don’t know if the plant gives off a special scent that attracts gnats or if they just land on the stems by accident, but it certainly solved my gnat problem!

I later learned that the bat-face cuphea is considered a “protocarnivorous plant.” A plant that traps and kills insects, but lacks the ability to directly digest the nutrients. Instead, the insect falls to the ground and microbes decompose it, freeing up the minerals that the plant can then absorb.

Eventually, of course, I planted my sticky little plant friends out in the garden where they bloomed abundantly all summer, much to the delight of the hummingbirds that just couldn’t get enough of them. So much nectar! But no ants clambered up the stem to steal the nectar. They ended up stuck at the base of the plant. Apparently, it’s a great plant for trapping aphids and whiteflies too, plus other tiny plant pests, although I can’t say I saw any other identifiable insects other than even more fungus gnats (yes, they live outdoors as well!).

I remember thinking, “An insect-trapping plant? What a great garden tool! Someone should market this!” But, as far as I know, nobody has. In fact, apparently hybridizers are hard at work developing a non-sticky Cuphea llavea, as dead insects clinging to a plant’s stem hinder sales.

For the next few years, I sowed bat-face cuphea seeds whenever fungus gnats showed up … and when you grow literally hundreds of houseplants, plus untold numbers of seedlings each spring, fungus gnat will show up!

Chiltern seems to have stopped carrying bat-face cuphea, although other seed houses still do. However, they do offer an even stickier if not (in my opinion) as a pretty cuphea: clammy cuphea or blue waxweed (C. viscosissima). The name viscosissima means, obviously, the stickiest! You can’t beat that!

Even Better

But I later found even better when it came to fungus gnat control indoors: butterworts (Pinguicula spp.).

Butterworts are true carnivorous plants (their leaves give off enzymes that dissolve insects) with curious sticky yet slippery stemless leaves forming a rosette. They’re a surprising yellow green, a shade that seems to attract many insects and certainly fungus gnats. And unlike bat-face cuphea, an annual that you need to restart often from seed, you can grow tropical or subtropical butterworts indoors year-round.

And butterworts are very attractive, too, looking much like a small African violet. Most, like the popular and easy-to-grow Mexican butterwort (P. moranensis), bear attract purple flowers over a very long season.

With butterworts, I find I can nip the infestation in the bud and keep it nipped. In fact, in general, I don’t even realize my plants have fungus gnats until a few blow their cover by sticking to the butterwort leaves. And with the butterworts eating them, the infestation stops there. Ideally, you’d place a butterwort among each grouping of houseplants as a fungus gnat preventative and certainly among the seedlings you start indoors in the spring.

I wrote about butterworts in the article Grow Your Own Living Sticky Trap! which you might want to consult.

Outdoors Too?

One has to wonder if growing plants specifically to catch insect pests can’t be done outdoors too.

There are, after all, hardy butterworts you can grow in temperate climates. Common butterwort (P. vulgaris), notably, is found throughout northern Eurasia and North America, including in Greenland and all provinces and territories of Canada. But butterworts do like a boggy environment, not something all gardeners have access to.

Might I suggest trying a catchfly (Silene spp.) instead? The very name says it: they catch flying insects. Most are perennials and certainly easy enough to grow.

The best-known species is sweet William catchfly (Silene armeria), native to Europe, but well established as a garden escapee in many countries, including in Canada and the US. Indeed, it’s often included in wildflower seed mixtures. Or try its North American insect-catching equivalent: sleepy catchfly (S. antirrhina).

Other possible insect-trap plants for the outdoor garden include:

• Clammy campion (Viscaria vulgaris, formerly Lychnis viscaria),
• London pride (Saxifraga umbrosa)
• Plumbago (Plumbago auriculata)
• Sticky cinquefoil (Drymocallis glandulosa, formerly Potentilla glandulosa)
• Sticky primrose (Primula glutinosa)
• Sticky sage (Salvia glutinosa)
• Tobacco (Nicotiana tabacum)
• Sticky tobacco (Nicotiana glutinosa)
• Tall cinquefoil (Drymocallis arguta; formerly Potentilla arguta).

And even the recently named insect-killer tobacco (Nicotiana insecticida). Read the article Top 8 Plant Species New to Science in 2021.

Who knows, you might be able to create a garden so dense with insect-trapping plants that bad bugs will recoil in horror at the very thought of visiting it!

Top illustration: creazilla.com, pngset.com & depositphotos, montage: laidbackgardener.com