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How Does A Monarch Butterfly Defend Itself From Predators?

Many different animals eat insects, and monarch butterflies are not entirely immune from being turned into a bird or spider’s next meal. But they aren’t entirely defenseless either–they have ways of protecting themselves. So, how does a monarch butterfly defend itself from predators? What kinds of predators does it face? Keep reading! In this article, we’ll answer these questions and more.

How Does a Monarch Defend Itself?

How Does a Monarch Defend Itself

Monarch butterflies have their share of predators, but they are able to limit the number of predators through a couple of different methods. These methods are aposematic coloration and toxicity.

Let’s take a closer look at each of these defense mechanisms.

Bright Colors

The monarch’s bright orange and black color scheme is called aposematic coloration. In the same way we learn to identify traffic cones and high-visibility vests in work zones, insects and animals learn that a monarch’s coloration is a warning of potential danger.

In essence, everything about a monarch’s wings loudly proclaims to would-be predators, “Stay away!”

And, in many cases, the predators do stay away. This is because they learn, either by instinct or past experience, that monarch caterpillars and butterflies are toxic.

Toxicity

Monarch caterpillars ingest toxins known as cardiac glycosides from the milkweed they eat. These toxins pass from the larvae to the adult butterflies, making both caterpillars and butterflies dangerous to many potential predators. 

The toxins can cause severe illness and vomiting in birds and any other animals that make the mistake of snacking on a monarch. 

Surprisingly, not all monarchs have the same level of toxicity. Female butterflies retain more of the toxin than males, though both sexes lose their toxicity as they age. 

Do Birds Eat Monarch Butterflies?

Most birds instinctively know to avoid the brightly colored butterflies, while others learn the hard way by getting sick after eating a monarch.

That said, there are a few birds who do eat monarchs; they appear to be immune to the toxin entirely, though some smartly eat only the parts of the butterfly with the lowest concentrations of toxin. These birds include:

  • Black-headed grosbeaks: These birds tend to hang out in flocks around monarch overwintering sites. They prey on monarchs by catching them on cold days (when they are less active); they will eat the butterfly’s body while leaving behind the wings.
  • Black-backed orioles: These birds also like to cluster at monarch overwintering sites and prey on the butterflies on cooler days. They tend to avoid eating the wings, but they will slit open the body, apparently sucking out the insides and gorging the thorax.
  • Eastern bluebirds: This bird frequently eats monarch caterpillars after squeezing out most of their insides. This squeezing action removes much of the toxins, leaving behind only the caterpillar’s skin, which will not harm the bird.
  • Shining bronze cuckoos: Monarchs in New Zealand and Australia frequently become the victims of shining bronze cuckoos, who appear to have a natural immunity to the butterfly’s toxin.

Certain types of wasps will also catch and eat monarch butterflies and may feed them to their young.

Do Monarch Caterpillars Get Attacked By Other Insects?

Do Monarch Caterpillars Get Attacked By Other Insects

Only one-tenth of monarch eggs survive all stages of their life to reach adulthood. This is because eggs and small caterpillars face many threats, as they have not yet absorbed enough of the toxin to protect themselves. 

What’s more, many insects attack and eat even larger monarch caterpillars despite their toxicity. These insects are apparently immune to the toxins. Some of the insects that prey on monarch caterpillars include:

  • Spiders: Though spiders are seen as beneficial in the garden, the flip side is that they will eat good insects as well as those we might see as pests. Many types of spiders will eat monarch caterpillars, and they often spin their webs on milkweed plants to make capturing them easy.
  • Fire ants: Fire ants are known for eating many different foods, including a variety of insects and bits of flesh from dead animals. They appear to suffer no ill effects from eating monarch caterpillars. 
  • Ladybugs: Another beneficial garden insect, ladybugs will not differentiate between “good” and “bad” bugs. They are often drawn to milkweed plants to eat the aphids that cluster on them, but they will eat monarch caterpillars as well.
  • Wasps: Paper wasps carry off monarch caterpillars to feed their young, and braconid wasps sometimes parasitize monarchs by laying eggs on them. The eggs then hatch and eat the caterpillar from the inside out, slowly killing it.
  • Stink bugs: Some types of stink bugs will eat monarch caterpillars as well. They do so by jabbing the caterpillars with their own toxin then sucking out the insides.
  • Milkweed bugs: Milkweed bugs eat the leaves and seed pods of milkweed plants, but they often end up ingesting monarch eggs and small caterpillars along with it. 
  • Tachinid flies: These flies are parasitoids, or parasitic insects, that frequently lay eggs in monarch caterpillars. As with braconid wasps, the fly larvae slowly kill the caterpillar as they eat it alive from inside.
  • Larger monarch caterpillars: Sometimes, larger monarch caterpillars will turn cannibal and eat smaller ones. They sometimes eat monarch eggs as well.

Monarch caterpillars are also frequently infected and killed by viruses, fungi, bacteria, protozoa, and microscopic parasites. 

Check out this video to learn more about efforts being made to identify monarch predators:

Conclusion

Monarchs have many predators, including some birds, insects, microorganisms, and parasites (and humans!). That said, they would have many more predators if they didn’t have their bright colors and toxicity to warn away many animals looking for a snack.

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