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Bug of the Week: Ants Visiting Extrafloral Nectaries

It is cold (for us) and windy this morning, and I wasn't sure I'd be able to find a bug of the week. No fear, there's always something going on in the insect world.

barrel cactus

First I checked our barrel cactus, which is covered with yellow fruit.

barrel cactus

As I got closer, I spotted a beige patch near the base of one of the fruit towards the right/center of the photograph. You'll be able to see it more clearly in the next photograph.


The biege patch looked soft and furry, with some yellow and orangish bumps.

ants at extrafloral nectaries

Ants were visiting those bumps in a purposeful way. First they would arrive looking slender.

ants at extrafloral nectaries

After spending some time with their heads near the bumps their hind portion, called a gaster in ants, would start to swell up.

ants at extrafloral nectaries

These ants are feeding at the extrafloral nectaries of the cactus. Nectaries are parts of a plant that produce the sweet juicy nectar. Many are found inside the flower of the plant. These structures are called extrafloral because they are outside of the flower.

Why does a cactus supply liquid sweets in the form of nectar to ants, especially in the desert where water is in short supply? There are several theories, including that ants increase the fertility of the soil around their mounds and ants are more likely to nest nearby when food is available, and/or that ants feed on insect pests while on the cactus. In any case, it is a fascinating example of just one of the complex relationships between ants and plants.

Thinking of sweets makes me want to have a cup of hot chocolate...

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