Missing numbers 1-20 worksheet with a fun caterpillar theme for learning.

The task is to fill in the missing numbers between 1 and 20 in the given sequences. Let's solve each row step by step.

Row 1:

```
1 _ 3 _ _
```
- The sequence starts with 1 and then jumps to 3.
- The pattern appears to be increasing by 2 each time.
- Therefore, the missing numbers are:
- After 1: \(1 + 2 = 3\) (already given)
- After 3: \(3 + 2 = 5\)
- After 5: \(5 + 2 = 7\)

So, the completed row is:
```
1 2 3 4 5
```

Row 2:

```
_ 7 _ 9 _
```
- The sequence has 7 and 9, which suggests an increase by 2.
- Therefore, the missing numbers are:
- Before 7: \(7 - 2 = 5\)
- After 7: \(7 + 2 = 9\) (already given)
- After 9: \(9 + 2 = 11\)

So, the completed row is:
```
5 7 8 9 11
```

Row 3:

```
_ _ 13 _ 15
```
- The sequence has 13 and 15, which suggests an increase by 2.
- Therefore, the missing numbers are:
- Before 13: \(13 - 2 = 11\)
- Before 11: \(11 - 2 = 9\)
- After 13: \(13 + 2 = 15\) (already given)

So, the completed row is:
```
9 11 13 14 15
```

Row 4:

```
16 _ 18 _ 20
```
- The sequence has 16, 18, and 20, which suggests an increase by 2.
- Therefore, the missing numbers are:
- After 16: \(16 + 2 = 18\) (already given)
- After 18: \(18 + 2 = 20\) (already given)

So, the completed row is:
```
16 17 18 19 20
```

Final Answer:

```
Row 1: 1 2 3 4 5
Row 2: 5 7 8 9 11
Row 3: 9 11 13 14 15
Row 4: 16 17 18 19 20
```

Thus, the final answer is:
\boxed{
\begin{array}{ccccc}
1 & 2 & 3 & 4 & 5 \\
5 & 7 & 8 & 9 & 11 \\
9 & 11 & 13 & 14 & 15 \\
16 & 17 & 18 & 19 & 20 \\
\end{array}
}