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Southern California, US and less than 1cm Please help identify this caterpillar.

host plant milkweed

enter image description here

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  • $\begingroup$ Are you sure the plant is milkweed? The flowers do not look correct. $\endgroup$ Commented Sep 2, 2019 at 0:30
  • $\begingroup$ Welcome to Biology.SE! For identification questions please edit your post to: 1) include the location (e.g. country and region — the more specific the better), and 2) an estimate of the size of the creature. The location and size can be essential clues for identification. ——— If possible clear, closeup photos of the open flowers on the host plant would also be helpful. ——— Please also take the time to go through the tour and then the help pages starting with How to Ask questions effectively on this site. Thanks! 😊 $\endgroup$
    – tyersome
    Commented Sep 2, 2019 at 5:29
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    $\begingroup$ I have the same caterpillar on yellow milkweed in San Jose CA and can't figure out what it is either! It doesn't look like traditional photos of tussock moth.... $\endgroup$
    – Lora
    Commented Sep 14, 2020 at 0:56
  • $\begingroup$ The milkweed looks like Asclepias curassavica, or tropical milkweed. In southern California, it won't die back in the winter, which can throw off the Monarch's normal migration and can cause a harmful parasite to build up. Please be sure to cut it back in the fall and throughout the winter, and consider replacing with a native species. $\endgroup$ Commented Aug 18, 2022 at 21:12

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Ok, firstly: That plant is not any type of milkweed i know, the flowers are too different. And secondly: That's not a caterpillar. It's a hoverfly maggot. Rather than grubbing about inside decaying roadkill or rotten fruit, hoverfly maggots are predators, actively roaming and searching for prey insects, which in this case would be those little yellow aphids on your plant. After a few weeks of devouring aphids, your little friends will turn into small, skinny flies that greatly resemble wasps(This is so predators leave them alone) and feed on nectar and pollen.

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    $\begingroup$ Well done, so +1! There’s even its food source on those leaves. However swamp milkweed and some others have narrow leaves and there appears to be a milky sap on a spot in the first picture right atop a vein. Since the flowers aren’t open yet (the sepals are right), it’s still possiblet that it’s a kind of milkweed. $\endgroup$ Commented Jun 5, 2022 at 13:07
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Hover Fly or Flower Fly larvae. Feeds on aphids which are most prolific on milkweed plants. They can eat small caterpillars, but aphids are primary. Flower flies feed on nectar and are pollinators. Not annoying house fly category.

Yes, that IS milkweed. Tropical milkweed brought from Mexico originally and therefore not native to the US. Considered bad for Monarch butterflies. Now banned from sale in California in 2022.

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    $\begingroup$ Welcome to Biology.SE. You are more likely to get a positive response to your answer if you explain why your identification is correct. Specifically, please edit your answer to add discussion of key features that led you to this conclusion and supporting references or at least validated images (make sure these are public domain). Without this your answer is indistinguishable from opinion. ——— Please also take the tour and then consult the help center pages for additional advice on How to Answer and How to Ask effectively on this site. $\endgroup$
    – tyersome
    Commented Aug 18, 2022 at 20:41

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