Short answer. No. Default is not allowed in these cases. Where the respondent fails to answer a petition for annulment, for declaration of nullity of marriage, or for legal separation, the court instead orders the State's prosecutor to investigate whether the parties are colluding.
What the law says
If the defending party in action for annulment or declaration of nullity of marriage or for legal separation fails to answer, the court shall order the Solicitor General or his or her deputized public prosecutor, to investigate whether or not a collusion between the parties exists, and if there is no collusion, to intervene for the State in order to see to it that the evidence submitted is not fabricated.
Rule 9, Section 3 — Default; [d]eclaration of. Read the full provision →
Why silence does not end a marriage case
In an ordinary civil case a defendant who does not answer can be declared in default and lose on the pleading alone. Marriage cases are carved out of that rule entirely. Where the respondent in a petition for annulment, for declaration of nullity, or for legal separation fails to answer, the court does not enter default but orders an investigation into whether the parties are colluding. The reason is that the State is treated as having its own interest in the marriage, so the case cannot be won merely because the other spouse chose not to contest it.
What the investigation looks for
Two distinct things. The first is collusion, meaning an agreement between the spouses to let the petition succeed, whether through silence, staged admissions, or an arranged failure to defend. The second arises if no collusion is found: the prosecutor intervenes for the State to see to it that the evidence submitted is not fabricated. So even a genuinely uncontested petition still faces a participant whose function is to test the proof. A petition that depends on the respondent not showing up is, for that reason, not a strong petition.
What this means for the petitioner
Expect the case to take longer and to turn on evidence rather than on agreement. A respondent who ignores the petition does not shorten the process, because the rule adds a step to it. You should be prepared for the ground you rely on to be established by proof that survives an adversarial check, because someone will be present to make that check even when your spouse is not. Planning the case around an uncontested hearing is the most common way this goes wrong.
And what it means for the respondent
Not answering neither protects you nor concedes the case. You will not be declared in default, so nothing is decided against you merely for staying silent. But you also have no voice in a proceeding that will determine your civil status and can carry consequences for property and for children. If you disagree with what the petition alleges, silence is the one response that guarantees your version is never placed before the court at all.