Concerning gender ratio of Monarch butterflies

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  • #53010

    Blake in Porirua

    I am perplexed and would love to hear of others experiences.

    The ratio of Males to females I am rearing is extremely concerning. 90/10 in favour of males. The over wintering butterflies really should be as many females as possible. or at least 50/50.

    Earlier in the season (nov- dec 2017) I had more females, probably 60/40. But since february 2018 the ratio is more like 10/90. Without checking my records or doing proper math, approximately every 18 butterflies I hatch there are only 2-3 females. I stockpile hatchlings for up to 3 days then release at local reserves in optimum conditions after feeding honey water.

    I have no hard evidence of why I have so many more males than females emerge. Things ive factored are than if chrysalis are inside then temp is more consistent, and not as much UV. Although i do try to take my inside chrysalis laden plants outside as much as i can manage on windless days. (wellington northerlies are extreme where I live).

    I have raised 150-180 monarchs over 2 seasons, not all tagged though. Most of the chrysalis are inside. Just before i think they will curl i take them inside onto my set plants. Something i am almost positive of is that butterflies from inside chrysalis are noticeably larger than outside chrysalis.

    Im looking forward to any confirmations or advice anyone may have.

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  • #53313


    My stats for this past season is as follows: raised inside from chrysalis stage.
    289f + 296m. Yes more late ones were males. I had a total of 750 for the season, but I was unable to record the gender of all of them. Caryl (Wellington)



    Yes lots more males born late in the season than female Monarchs.
    It was 3 males to 2 females earlier in the season.


    rob cooper

    yea carol we about the same maybe a few more girls this year we will get 220 away but sex very close



    If the butterflies emerge (or eclose) indoors you will appreciate that it is more like summer than winter weather We like our houses warm ! So the trick is to make the butterflies sense that it is not necessarily the same weather outdoors If it was mid summer they still don’t feed until 4 to 6 hours after eclosing – so as it’s cooler and darker there is no need to feed them Just let them go in a sheltered part of the garden and they will do what comes naturally



    Hi Jacqui
    Early in the season I had a very poor rate of caterpillars, with many dying. I thought of all sorts of reasons why but nothing I did worked. I have noticed all through the season that many of the cats were quite thin, despite there being plenty of food, & these thin ones did not do very well, either inside or outside. Over the last month with rotten weather threatening I brought in about 100 chrysalids & Js, & almost all have hatched with a reasonable 50:50 ratio of males/females. I note that there are still cats outside, even one very tiny one, but these will have to take their chances; in the past I have tried raising late cats with very little success.
    but the weather is not very good for them. Had the tiniest ever butterfly hatch today, main wings each less than 1” long, but quite vigorous.
    I try to release the butterflies on the day they hatch, unless very late in the day. Should i hold them over a bit longer & feed them before release?



    Interesting posts! Thank you. Looked at the number of males and females over past 3 seasons in Seatoun, Wellington.
    2017 – 2018 292 males 288 females
    2016 – 2017 108 males 101 females
    2015 – 2016 193 males 199 females




    Forgot to add that this year I have had some very small butterflies that seem just as healthy as the big ones. All reared in the same place.



    Hi Blake
    I’m in Auckland and have noticed similar to you.
    All my cats and chrysalis are outside but most are protected from weather extremes as most of them are in “monarch mansion’ on my deck under cover protected from westerlies and southerlies.
    Early on I had a fairly even ratio of butterflies – about 150 in total then in late Jan and February very few butterflies and eggs – I even had some kind folks in CHCH courier me up some eggs.
    Since Late March/ beginning of April I’ve had 50 eclose and the majority seem to be male although I have noticed more females in the last week or so. Still have lots of cats and 50+ chrysalis’ so hoping for lots of girls to overwinter.



    since march I’ve had 6 females and 5 males. Had a few fails which I didn’t take note of sex but seems close to 50/50 here in Karori.


    Blake in Porirua

    So an update…
    The last 22 butterflies were 20 female 2 male… very odd.
    I am going to say that I do believe weather makes a difference as to ratios, and I also have the theory that the later in the season it is (therefore getting colder) the more females there are. And that early in the season (mine started in early December) there were a few more females as well, perhaps 65/35. That’s just my two cents from observations. Surely as Mother Nature has designed these creatures with such an astonishing lifecycle, you’d think there is something more than luck involved.

    I just saw the other day that you can sex the chrysalis…. !!



    For what it’s worth, I have small numbers but a few more females than males so far. I’ve been mostly keeping them indoors in a (usually) warmish house. Right now I have one of each, waiting for a better patch of weather, and 10 chrysalides I haven’t sexed yet because I can’t find my magnifying glass. >.<



    HI Blake

    It has happened to me too in the past (huge imbalance about ten years ago) and I wrote to the international discussion group about monarchs. One of the key scientists told me that there was no good reason why this happens. However… I have my doubts, especially since in February there were very few female monarchs visiting – and a large number of the eggs that they laid were infertile. At a time when I should have had hundreds of caterpillars, there were only one or two!

    Will keep you posted if I find out more.



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