How Many Mealworms Should I Feed Bluebirds a Day?

The short answer

• For a pair of bluebirds feeding a box of nestlings, the North American Bluebird Society (NABS) says about 100 live mealworms a day is adequate: half in the morning, half in the afternoon.
• NABS gives no count for adults outside nesting. The 15 per bird figure comes from sialis.org, which credits it to Fawzi Emad and uses it as a limit for occasional treats. Two adults is about 30.
• Use live worms only for nestlings. NABS says never to give them freeze-dried worms, because food is a nestling's only source of water.
• At 2 to 5 cents a live worm, 100 a day costs $2 to $5. Across the 17 to 19 days NestWatch gives for the nestling stage, that is about $34 to $95 a brood.
• Mealworms are low in calcium. Shake them in a bag with calcium carbonate or calcium citrate powder, or offer sterilized eggshell. Start the feeder about 25 ft from the box and move it out to about 100 ft.

For a pair of bluebirds feeding a box of nestlings, about 100 live mealworms a day is enough. That is the North American Bluebird Society's figure: half in the morning, half in the afternoon. Two adults with no young need far fewer. The 15 worms per bird you will see on many pages is a limit for treats, and it does not come from the society. At 2 to 5 cents a live worm, the nestling weeks cost $2 to $5 a day.

What a mealworm is, and what "a day" means here#

A mealworm is not a worm. It is the larva of the darkling beetle, Tenebrio molitor. The North American Bluebird Society (NABS) calls it a nutritious supplement that bluebirds relish. You can buy it live, or freeze-dried, which means dried hard with nearly all the water taken out. The general guide to buying and keeping both is on mealworms.

A nestling is a chick that is still in the box and cannot fly. Once it leaves, it is a fledgling. The difference matters because NABS gives its count for one stage only: "a pair of bluebirds with a box of nestlings."

So "a day" is not one number. It depends on who is eating.

How many worms a day, by stage#

Read the rows this way.

Two adults outside nesting. NABS gives no count here. It says to offer worms "in limited quantities, just once or twice a day." The only number in print is 15 per bird, from sialis.org, so a pair is about 30. That page says to offer worms then "as an occasional treat, or during bad weather or for a widower." It is a ceiling, not a target.

Poor weather. NABS lifts the once-or-twice rule "unless poor weather conditions dictate more frequent feeding." Its list of reasons to feed includes the times "when weather conditions prevent the parents from finding insects." It gives no count for these days.

A pair with nestlings. NABS: "A hundred or so worms offered per day (half in the morning, half in the afternoon) should be adequate." That is for the whole family, not per chick. The 2012 draft of the same sheet said 100 "would be more than adequate." Both versions treat 100 as enough, not as a minimum.

Live worms only once there are nestlings#

This is the rule people miss. NABS says it twice: "Never supply freeze-dried mealworms as a food source for nestlings!" Food is a nestling's only source of water. Freeze-dried worms hold little moisture, and the sheet says a diet of mostly dried worms "could be harmful to nestlings."

Outside the nesting season, dried worms are fine. NABS says some people find them the cheaper choice. Bluebirds may ignore them, though, "unless other options for food are limited." Soaking them in a little water or vegetable oil may help. The full trade-off is on live vs dried mealworms.

What a brood costs, worked through#

Take a pair whose box has just hatched. Suppose you follow NABS and put out 100 live worms a day, 50 at breakfast and 50 in mid-afternoon. Price them at this site's working range of 2 to 5 cents a live worm.

1. One day is 100 worms. At 2 cents that is $2. At 5 cents it is $5.
2. NestWatch gives 17 to 19 days for this stage of an Eastern Bluebird nest.
3. Fed every day, that is 1,700 to 1,900 worms for the brood.
4. The bill comes to about $34 at the low end (17 days at $2) and $95 at the high end (19 days at $5).

Now the same pair outside nesting, at the 30-worm treat limit:

NestWatch adds that the female often builds a second nest after a brood fledges. If she does, run the sum again.

The gap between the stages is the point. Feeding nestling numbers all year costs more than three times as much as the treat limit. It also teaches starlings where the food is. The ways to keep them out are on mealworm feeders.

Where "15 per bird" comes from#

Search the question and 15 per bird comes up near the top of the results. It traces to sialis.org, a bluebird site. Its mealworm page says: "Fawzi Emad recommends offering about 15 mealworms per bluebird per day." It also says to keep to "no more than 15 mealworms per day, per bird."

The NABS sheet has no per-bird figure at all. Its only number is the 100 for a pair with young. Sialis.org quotes that NABS line on the same page, a few lines away, so the two sit side by side and are easy to mix up.

So both numbers are real, and they answer different questions:

• 15 per bird is a limit for treats, when insects are plentiful and nobody is feeding young.
• 100 per pair is what NABS calls adequate for parents with a box of nestlings.

The mistake is using the first one for the second job. Thirty worms for a pair with a box of young is under a third of what NABS says is enough. This site's own feeder pages use 15 per adult as their everyday cap, and that is the case it fits.

Where to put the feeder, and how to move it#

NABS gives the steps:

1. Start close. Put the feeder about 25 ft from the nest box.
2. Draw their eye. A flat saucer with a few worms on top of the feeder helps bluebirds notice it. Once they know the routine, put the worms inside.
3. Move it out bit by bit, to about 100 ft, as the birds get used to it.
4. End where you can watch. Ideally the last spot is one where you can see them feed.

Sialis.org gives the reason for the distance. It puts the feeder about 100 ft from a box "so predators and nestbox competitors are not attracted to the box."

Use a dish with smooth sides, such as glass, ceramic or a tuna or cat food can, so live worms cannot climb out. NABS rates a hopper with an entry hole at each end as the best design, with a cage feeder as the other choice. Both keep larger birds out. Worms on the ground tend to burrow or go to robins.

Calcium: the part a count does not fix#

Mealworms are rich in fat and protein, but NABS says they "do not provide a complete diet." They are low in calcium. A diet of only mealworms could leave nestlings short of calcium, perhaps with weak bones, or cause egg binding in laying birds. Egg binding is when a female cannot pass an egg.

NABS gives two fixes:

• Dust the worms. Put them in a plastic bag with calcium carbonate or calcium citrate powder and shake gently to coat them. Health food stores and online shops sell both.
• Use eggshell. Some people sterilize eggshells, dry them and grind them to a powder to use with the worms. The oven method this site uses is on spring bird feeding.

NABS also names black soldier fly larvae as a supplement that is naturally high in calcium, unlike mealworms.

What this answer does not cover#

The 100 figure is for a pair with "a box of nestlings." NABS does not scale it by the number of chicks, and it gives no count for an incubating female, for fledglings or for winter. The 15 per bird limit is one person's advice, passed on by sialis.org. It is not a measured intake. The 2 to 5 cent price is this site's working range, not a market survey. Sialis.org quotes bulk mail order at about $40 per 10,000 worms plus shipping, which is about 0.4 cents a worm, but that page is undated, so price your own supplier. The NestWatch days are for Eastern Bluebirds. Western and Mountain Bluebirds were not checked. None of this replaces the wild insects a pair should still be finding. NABS warns that worms alone will not bring bluebirds to a yard that does not already have them. What helps and what does not in the nesting weeks is in feeding during nesting season, and the habitat side is on the Eastern Bluebird profile.

Frequently asked questions#

How many mealworms does one bluebird eat a day?

No source we found counts what one wild bluebird eats in a day. The figure you will see is a limit, not a measurement: sialis.org credits about 15 worms per bluebird per day to Fawzi Emad, and says to keep to no more than 15 per bird when worms are a treat. The same page notes seeing each bird eat about 3 to 10 worms per visit. Wild insects are supposed to be most of the diet.

How many mealworms do I need for bluebird babies?

About 100 live worms a day for the pair, according to the North American Bluebird Society, split into a morning and an afternoon serving. That figure is for the whole family, not per chick. NestWatch gives 17 to 19 days for the nestling stage, so one brood works out to roughly 1,700 to 1,900 worms if you feed every day. Feed live worms only to a pair with nestlings: NABS says never to give nestlings freeze-dried worms.

Can I feed bluebirds dried mealworms?

Outside the nesting season, yes. NABS says freeze-dried worms are low effort and may keep longer, but bluebirds may ignore them unless other food is short, such as in bad weather. Soaking them in a little water or vegetable oil may make them more attractive. Once there are nestlings, switch to live. Food is a nestling's only source of water, and NABS says a diet of mostly freeze-dried worms could harm them. The trade-offs are on live vs dried mealworms.

Should I feed bluebirds mealworms in winter?

In cold places, a little helps. NABS says small birds that stay the winter, such as bluebirds, chickadees and nuthatches, appreciate a small hanging cup of mealworms. It also lists getting birds through severe weather as one of the reasons to offer worms, and says to feed more often than once or twice a day when the weather is poor. It gives no winter count, so keep servings small and put them out at fixed times. The rest of the cold-weather routine is in winter bird feeding.

Will putting out mealworms bring bluebirds to my yard?

Probably not on its own. NABS says that if you have never or rarely seen a bluebird in your yard, chances are they will not show up just because you put out worms. Other birds will find them first. Worms work best to keep bluebirds you already have. To make the yard suit them, start with the Eastern Bluebird profile.

When should I stop feeding mealworms to bluebirds?

NABS does not set an end date. Its reasons to feed are specific: to draw a pair to a box, to help an incubating female, to back up the nestlings when weather keeps insects down, to cover a missing parent, and to help birds through severe weather. When none of those apply, you can cut back to the occasional treat, or stop.

Sources and further reading

1. NABS Factsheet: Mealworms (revised June 2021) North American Bluebird Society, hosted by the New York State Bluebird Society A hundred or so worms a day, half morning and half afternoon, adequate for a pair with a box of nestlings; once or twice a day unless poor weather; never freeze-dried for nestlings; calcium carbonate or citrate dusting; feeder about 25 ft from the box moved out to about 100 ft
2. NABS factsheet: Mealworms (draft, 24 May 2012) North American Bluebird Society Earlier wording: a hundred or so worms offered morning and evening would be more than adequate for a pair with a box of nestlings
3. Feeding Mealworms to Bluebirds sialis.org Credits about 15 mealworms per bluebird per day to Fawzi Emad; limit to no more than 15 per bird per day as an occasional treat; feeder about 100 ft from a nest box; each bird seen eating about 3 to 10 per visit; undated
4. Eastern Bluebird: nesting facts NestWatch, Cornell Lab of Ornithology Clutch 3 to 5 eggs; incubation 11 to 19 days; brooding period 17 to 19 days; the female often builds a second nest after a brood fledges