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I have heard that the Human Botfly transfers its eggs through other invertebrates, and it strikes my curiosity that if an insect could simply land on its host directly to deposit its eggs, then why have intermediate hosts?

I have speculated that the vectors may be better specialized for penetrating hosts, and that penetrating hosts may be difficult, or that approaching hosts is risky. Another speculation on my part is that the Human Botfly may be filling a niche where it does not need to compete.

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    $\begingroup$ Possibly for the same reason as indicated here youtube.com/watch?v=a9qtVbgDnsU. Using a smaller intermediary is less noticeable and threatening to the host. $\endgroup$
    – Martin Smith
    Aug 28, 2015 at 21:18
  • $\begingroup$ could not access Google book link . $\endgroup$
    – Always Confused
    Oct 15, 2016 at 13:54
  • $\begingroup$ Strange - me neither (I think I could when I tried a couple of months ago, though). I can access the previous page (with the first few lines of the section "Parasitism by courier") which confirms it's the correct link. $\endgroup$
    – arboviral
    Nov 4, 2016 at 9:11
  • $\begingroup$ I recently could not find the link either, but question is still open for a cited answer. $\endgroup$
    – Galen
    Dec 6, 2016 at 0:10

1 Answer 1

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In multi-host complex life cycles (CLCs), an intermediate host often aids in the dispersal of offspring.

In general terms, an animal, say a botfly, have an ultimate "purpose" or 'goal' to spread their genetic information as much as possible. This could mean producing a large number of offspring and hoping some survive or it could mean having one offspring, investing a lot of energy and ensuring it does survive. Regardless, spreading genetic information often requires offspring to disperse (or be spread) a great distance, which may allow the individuals' genetic information to dominate an new region.

In the case of botflies, having an intermediate host means the genetic information can be spread a great distance.

If you're looking for a more thorough explanation of complex life cycles, this paper describes it well. There is also this site more specific to the botfly which is not peer reviewed, but well-researched and descriptive.

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