Does the Castor Bean Plant Attract Insects?


Castor bean plants, also known as Ricinus Communis, are beautiful! And yet, while being one of the most poisonous plants out there, for some reason – the flowers do not deter or kill bugs. I became curious as to why.

The leaves, stem, and seeds all contain the deadly Ricin, one of the deadliest toxins known, which is supposedly 6,000 times more poisonous than cyanide and 12,000 times more poisonous than rattlesnake venom.

This plant can grow up to 12 feet high and has big, beautiful star shaped leaves. This plant was believed to have originated in eastern Africa and is used worldwide for an industrial lubricant, preservative, and even herbally. But if the rest of the plant is poisonous, what about the flowers?

Flowers of the Castor Bean Plant

I decided to plant a castor bean plant next to the side of my house this year. I believe the one I have is called a “Red Spire”. They prefer full sun and thrive in humid conditions and are just very lovely to look at. I’ve been observing it this year.

Some of the research I’ve done online would suggest that this plant is avoided by insects because it’s toxins, specifically mosquitos. However, I have found other research that suggests these plants, in fact, attract predatory insects such as wasps, ants, and bees which is probably why it’s avoided by other insects!

I noticed when the japanese beetles would eat the leaves, they died. Almost immediately. So I did not observe any more japanese beetles feasting on this plant as I’m sure the dead ones deterred those others.

However, I have observed that the flowers of the castor bean plant attracts all sorts of insects; from ants, to bees, flies, and wasps. They all seem to feast on the nectar of the castor flower, almost in complete harmony with one another.

The wasps do seem to display aggressiveness towards each other, almost territorial. This leads me to believe that the flower is the only part of the plant which does not contain the deadly ricin. I have to wonder, with the behavior displayed by the wasps, if the nectar doesn’t seem to be like a drug to them. These insects are just covering the flowers from morning till night. When wasps are usually traveling back to the nest during dusk, the ones on my castor bean plant just seem to carry on and stay on the flower.

So suffice it to say, the castor bean plant DOES attract insects – the predatory kind, and while they do not feed on the leaves, stems, and seeds – they do love the nectar of the flower.

This nectar is produced by extra-floral (outside the flower) nectar glands. The flowers do not have actual petals. There are female and male flowers that are produced. The male flowers shed large amounts of pollen which is distributed to the female flowers by the insects to pollinate them. The plant relies on this therefore the nectar I believe is not only highly seductive to these insects, but almost addictive.

Only the female flowers develop into a seed capsule. The seed covering gradually turns to brown when mature. The covering protects the seed so it is okay to touch, but DO NOT touch the seed inside with bare hands. This is covered in ricin which is a high irritant on the skin unless very diluted. This seed is also highly toxic so should not be ingested.

These seeds can be harvested and kept in a cool, dark place over winter (for those of you who live where there are harsh winters) and re-planted in the spring to produce more plants. Soak the seeds overnight for better germination. Seeds should be planted 1-1 1/2 inches deep. You should see some growth in as little as 1-3 weeks. This plant grows quickly.

I did find an interesting study done by the Journal of Evolutionary Biology Research:

Castor bean (Ricinus communis L.) is a myrmecophytic plant species with specialized extrafloral nectar
(EFN) glands that serve to attract predatory insects, which in return defend plant-tissues against
herbivores. The EFN glands on castor bean plants are located along the leaf petioles as well as on the
peduncles of its imperfect (unisexual) flowers. This field-project evaluates the richness, diversity, and
species assemblage of insects visiting EFN glands located on (female and male) flower peduncles and
leaf petioles on castor bean plants growing in a Southern California coastal landscape. We detected
that EFN glands on female-flower peduncles were visited by an insect community that was distinct from
that of the other two EFN gland types on castor bean. Additionally, the insects visiting EFN glands on
male-flower peduncles more closely resembled those observed visiting EFN glands on leaf petioles. We
conclude that the observed differences in the biotic defense of foliar and unisexual floral tissues on
castor bean are congruent with the optimal plant-defense strategy of a monoecious pioneer species.”

So be aware, if you are going to plant the castor bean plant in your yard, it will attract wasps.

Castor Bean Plant as a Herb


Ricin is water soluble, so it is not released during the pressing process of the seed that is used to make the castor bean oil.

Castor bean oil has been used for centuries medicinally and can be ingested (not in large amounts!). It has been used as a remedy for constipation to heartburn. It is an effective laxative, and can also be used externally as an emollient for dry skin or if you make your lotions, as a base. Although I would warn you, castor bean oil is VERY thick. So thick, it’s been used as an effective treatment against scabies by suffocating them. I’ve also seen studies where castor oil was effective in growing hair, even eyebrow hair, when applied externally.

I would never personally suggest ingesting castor oil as there are other better herbal alternatives to treating constipation and heartburn, but I have found castor oil to be a really good emollient/carrier oil for mixing with essential oils.

Check out my blog on making a fantastic insect repellent using castor oil Here.

Starwest Botanicals sells some really good organic virgin castor oil.

All pics and videos on this site are ones I’ve taken of my castor bean plant. 

References: Master Gardener Program, University of Wisconsin

Journal of Evolutionary Biology Research

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